These days it seems that the 'flaming Mono war' has raised to a new DEFCON level. For me, I think that it's silly to avoid this very good framework.
Anyway, it's also good to discuss it and go deep into legal diatribes... if they remains polite.
I had read thousands of words(yes, sometimes good and honest) against the framework, but today I've finally read this excellent post titled Here we go again – why Mono doesn’t suck.
I can only suggest you to read it too, now.