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.
.... This is not to say that implementing C# is a bad thing. ... [writing and using applications in mono] is taking a gratuitous risk.
twitter writes: "There's been a lot of fuss about mono lately. After SCO and M$ suing over FAT patents, you would think avoiding anything M$ would be a matter of common sense. RMS now steps into the fray to warn against a serious mistake.