Earlier quoted context omitted.
What would be wrong having a Microsoft account to log in exactly? They aren't getting any more information from you then they have currently purchased. I remember when I had a YouTube account, a blogger account and a Google account and I am glad I just use one google account myself.
Microsoft accounts are a trainwreck... I've got at least three or four of them all with the same email address, and despite years of effort to link them together and consolidate, I still have to use all of them to log into different services and access different resources. The permissioning on things like Azure and VSTS doesn't make a lick of sense.
I'm actually really excited about MS+GitHub, but have to agree the account situation sucks.