In short, we are in an adversarial situation. Microsoft does not want us to succeed. Thus we cannot trust Microsoft, even if we'd like to, and must consider Mono based upon the question "What is the worst thing MS can reasonably do?". We can only trust Mono if we are convinced Microsoft doesn't have weasel room. The current situation appears, to me, to have lots of weasel room. The technical merits of Mono are basically irrelevant if its a trojan horse in the long term.