As far as "playing catch up with a moving target", I don't see how that's terribly relevant, the end result is still a platform that continues to improve and advance. If the C# code that runs on Windows and mono is still more advanced than, say, Java or Perl, and continues to advance (even though not as fast as C# on Windows alone) then that's still a benefit. Given the advent of monotouch and the coming of monodroid it seems like even a hard-core MS hater could come to appreciate C#.
The problem is that it's not. You can do anything you want when it comes to SaaS using python, ruby, php, node or java. Actually those have huge open source communities with tons of libs available to make work faster. This is not the case of C# and if it ever gets there, it probably won't be any better. So again, I don't see any reason to use it, and plenty of reasons not to and being a "hard-core MS hater" would probably come at the bottom of the list of reasons not to use C#, don't try to justify the lack of interest in MS by some kind of imaginary persecution. But to each his own , if you're happy with it go for it.
Some of them also believe Python, Ruby etc are for kiddies :)