In fact, I think there's a strong 'once a criminal, always a criminal' mentality that takes a healthy skepticism to an unreasonable level. At least with the benefit of the doubt you can be wary of what Microsoft's intentions really are, but I don't think it's productive to go 20 years into the past and pretend that absolutely nothing has changed since, and rehashing everything from that time as if it only happened yesterday. It's an unreasonable standard and if nothing else, it presents the self-fulfilling prophecy where you're only satisfied once you've found proof that Microsoft today hasn't changed at all. So you've practically doomed GitHub to fail post-acquisition because you've already decided it _will_.
I'm not sure why you'd want that. So on that level I hope that Microsoft doesn't betray the gigantic community that has built around GitHub, which itself has taken open source to a whole new level. It's an appeal to emotion, I know, but I just don't see the value in being straight up negative in the light of recent evidence that suggests the contrary. You would never hold yourself to such an unforgiving standard (unless you wanted to sacrifice yourself on the altar), so it's better to give it a chance instead of throwing out the baby with the bathwater.
(Secretly, I'd love it if they, for example, rethought the pricing strategy and offered free private repos the same as every competitor does.)
That said, it's a little worrying that tech is continuing to consolidate around the giants.