I guess the thing that concerns me (not speaking for anyone else) has largely been the (admittedly late) realization that Github can be bought.
I had, for some indiscernible reason, thought of Github as this near-benevolent entity that existed exclusively to facilitate open-source and distribute Octocat stickers. When they were purchased by one of the largest megacorporations on the planet, it pulled-back the curtain, and showed that, no, they are a for-profit business, not a charity.
I shouldn't have thought that way, but I did, and as a result the MS-buying-Github thing has not sat well with me.