[patcito]

> I don't get it. Why is the GNU Project developing their own C# implementation but is seemingly anti-Mono?

Did you read the article? Having a free C# implementation is important because it allows people to run their C# program on free platforms according to the FSF. However, writing and distributing apps in C# is not encouraged as people might get sued. RMS points that he has nothing against mono or any other free C# implementations (proof is that GNU has its own Portable.NET) as it allow people to move to a free platform.