because Linux is faster

I strongly doubt that a PC will work faster after installing Linux. If you install a mainstream distribution (like Linux Mint or Ubuntu) with the default settings today, then your pc better had enough memory and processing power. Modern Linux distributions have 'modern' requirements, just like this is the case with other operating systems.

It is true that you can make old PCs useable again with Linux. But only if you have enough experience to select and configure a distribution. If your distribution is fast and has a small memory footprint, this is probably at the expense of usability.

because you can install it quickly

It doesn't matter that you can install Linux quickly. There is already an operating system on your PC. This is always faster than setting up something new.

because open source software is more secure

Since Heartbleed, Shellshock and Drupageddon we know that open source software is vulnerable just like any other kind of software. I do believe that chances on errors in the source code become smaller as more people look at it. But the source code being availabe, doesn't guarantee that peple are actually looking.

I found Shellshock very impressive: this vulnerability has been a documented feature in bash for more than 20 years. During those 20 years, simply no one noticed that this feature could be abused for unwanted things.

I often made fun of Windows' security in the past. And I was probably right at the time :). But Microsoft has come a long way. I believe that the architecture of Windows 7 is such that you can configure it in a secure way.

But, as with Linux, a system is only as secure as you configure it. Windows is often criticized because it's very easy to get administrator privileges. But with Ubuntu and derivatives, the process isn't a lot different. And imagine that you install Puppy Linux because you're looking for a quick distribution, you log in as root by default.

If you use Linux, you generally don't need Antivirus software. Well, if you keep your Windows OS up to date, and you use Windows with a non-administrator account, and you have some basic knowledge about how the Internet works, I think you can nowadays run Windows without antivirus software. Antivirus software doesn't work as good as it used to anyway, because a lot of viruses today are smart enough to encrypt themselves.

because it is more stable

On the server, maybe. But most of the people you want to convice to use Linux are not going to set up a server. At best, they want to try it on their laptop. But if they - just to say something - have an nVidia graphics card, I dare say that stability might be an issue.

because you get free support from a fine community

If you have a question about Linux, just ask Google. Google usually takes you to a discussion on Stack Exchange, and then you find the correct answer. Chances are you do. Chances are you don't. It depends.

But - do not tell anybody - if you have a question about Windows, this approach probably works as well. And I suspect that this is also the case for Android and Apple-OSes.

And although I've had many positive experiences in open source communities, it is certainly not always a bed of roses. Sometimes people can be very brutal, as Lennart Poettering says in a rant on Google+. I won't pretend that Poettering always behaves exemplary, but even if he doesn't, this cannot be an excucse for others bad behaviour.

because you need to fight Microsoft, the great enemy

This is not really an argument from the pages that I found through the various search engines, but it is one that I often used in the past. And in that past I was right without doubt :-)

But today this is no longer the case, I think. The days when Microsoft was the only player on the market, are over. I just had a look on the user stats for the website of the non-profit organization I work for. Windows' share is only 65%. IOS (iPhone and iPad) accounts for 15%. Macintosh and Android take both 9%. Windows is not alone any more, and Microsoft knows this very well.

In recent years, Microsoft is investing more in interoperability and open source. In the near future you will be able to host ASP.NET web applications on a Linux Server with Mono. Today there is Microsoft Office software for Android and IOS. A fair amount of .NET libraries developed by Microsoft (like Entity Framework and ASP.NET MVC), are available under the Apache 2 open source license. It would not surprise me if Windows will eventually given away free as in beer, just like Android.

Granted, Microsoft is still a monster with multiple heads. While one of the heads is friendly towards the open-source community, another head is sueing projects over software patents. Jeremy Allison of the Samba project, told at FOSDEM 2013 that he worked together with Microsft on Samba 4. On the other hand, he was very happy that he could come to Brussels for once to speak at FOSDEM, instead of having to deal with judges.

Nevertheless, I think Microsoft is slowly changing. I hear more positive stories than before. Microsoft is no longer the enemy to fight. That time has passed.

The companies that you should keep an eye on today, are Apple and Google. I hear more disturbing stories about those than about Microsoft. I might tell you more about this another time.

because you have everything: Thunderbird and LibreOffice

I hear this too often. "All the necessary software is available, for example, Thunderbird and LibreOffice."

Seriously? Office and e-mail? Is that what you need? In 2000 perhaps, but today? I think not.

Office is the thing that you don't need. If you do your work in Office, or in your mail client, then I think you're doing it wrong. What you need is a browser, a document reader and a decent text editor. And if you insist, maybe a spreadsheet. If you've got those tools, you're ready to go.

Do not put any emphasis on LibreOffice. If you're talking about LibreOffice, people will compare it to Microsoft Office. And Microsoft Office is more streamlined, like it or not.

But really, that's not relevant. You don't need an office suite today. If you insist to do something like Microsoft Office, use Google docs. But I think there will always be better solutions.

A wide range of easy to install software

If you install a mainstream Linux distribution, you have access to a very wide range of software packages, via the so-called software repository. You can compare this with an app store. You want to install an application to edit photos or audio? You need a programming environment for any programming language? You can download and install all this automatically.

Today, there are many app stores around. But I have the impression that the quality of the applications in Linux software repositories is generally higher than the quality of, for example apps in Google Play. Applications in a repository certainly contain significantly less ads. And they are easy to update. Did you ever use Java or Flash on Windows 7? Then you know the pop-ups asking you to update. But updating doesn't work, because the installers don't ask for elevated permissions. If you hate this as much as I do, try Linux Mint, and be delighted.

A system that's consistent and mature

If you install a mature Linux distribution, you end up with a nice consistent system. You've got a text editor, a sound recorder, a document viewer, a web browser, and so on. In most of the cases they have more or less the same look and feel. Of course you are free to install 100 different sound recorders if you want to, but after a standard install you have one, the one that the distribution likes the most.

I wanted to mention this explicitly, because this is not the case for Windows 8.1. There you have two document viewers: one for the desktop, one for Metro. Two sound recorders: one for the desktop, one for Metro. Two web browsers. And I could carry on.

Windows 8.1 is young. Windows 10 will probably be more mature. But if you want a mature Linux distribution, there is plenty of choice today.

No crapware

Did I tell you that your operating system is installed as good as for free when you buy a new computer? What I forgot to tell, is that very often a lot of other software is installed for free as well. A lot of software you actually don't want or need. (Maybe this is less the case for Apple products, but they are also less 'as good as for free'. :))

I bet you've seen them before: those programs that do who-knows-what, and start to complain after a certain amout of time that you have to purchase a license. Maybe this software also provides information about you to some third party, it's hard to tell. And removing it is not always easy, because it is often unclear what exactly is required to use your PC and what isn't.

A Linux distribution is almost never preinstalled. So you have to go through a tedious installation procedure. But after that, you have this clean system without crappy software. That alone makes up for the inconvenience of installing.

Easy reinstallation

If for any reason you need a complete re-install of your PC, Linux is the easiest solution. You download an image, and you get started without having to search for a license key.

Free software rules

This is the number one reason to try Linux: Linux is free software. And the vast majority of the applications that come with a Linux distribution, is free software too. When you install free software, then by definition you have access to the source code of the software. This means that you can check whether that software doesn't do things you do not want. Or, if you do not like studying source code, you can let an independent party check it out for you.

If you use software without having access to the source code, you have to trust your supplier. Does the software things where you are not aware of? Does it open a backdoor into your computer so that instance X or Y can check whether you behave well? Can that instance also turn off your computer if you don't behave? And to what extent are backdoors secured against crackers with malicious intents?

Obviously I did not read the source code of all the software I use. I do not compile all my software myself, to be sure that the software was effectively created from this source code. But the fact that I know it can, brings me some peace of mind.

Nowadays, more and more devices can be connected to the Internet. Phones, watches, home automation, cars... I wouldn't be happy if my car doors could be opened because of a hidden backdoor in the software.

The only way to keep an eye on the behaviour of your devices is using open source software. Unfortunately, I cannot choose which software is used in my car. But on my PC, I can. And I'd like to defend this freedom as long as I can.