Why free software shouldn't depend on Mono or C#
by Richard M. Stallman
Debian's decision to include Mono in the default installation, for the sake of Tomboy which is an application written in C#, leads the community in a risky direction. It is dangerous to depend on C#, so we need to discourage its use.
The problem is not unique to Mono; any free implementation of C# would raise the same issue. The danger is that Microsoft is probably planning to force all free C# implementations underground some day using software patents. (See http://swpat.org
.) This is a serious danger, and only fools would ignore it until the day it actually happens. We need to take precautions now to protect ourselves from this future danger.
This is not to say that implementing C# is a bad thing. Free C# implementations permit users to run their C# programs on free platforms, which is good. (The GNU Project has an implementation of C# also, called Portable.NET.) Ideally we want to provide free implementations for all languages that programmers have used.
The problem is not in the C# implementations, but rather in Tomboy and other applications written in C#. If we lose the use of C#, we will lose them too. That doesn't make them unethical, but it means that writing them and using them is taking a gratuitous risk.
We should systematically arrange to depend on the free C# implementations as little as possible. In other words, we should discourage people from writing programs in C#. Therefore, we should not include C# implementations in the default installation of GNU/Linux distributions, and we should distribute and recommend non-C# applications rather than comparable C# applications whenever possible.