It gives bad ideas a breeding ground to foster and you'd never even know about it. By publicly prohibiting speech all that happens is it is brushed under a rug and people pretend it doesn't exist. That doesn't make the problem go away, it's the same as shutting your eyes and covering your ears and pretending the monster in front of you no longer exists. If you get to define certain speech as unspeakable you justify the censorship of any speech determined to be unspeakable when you lose power and someone else steps up to the plate. As history has shown - it's a matter of "when" not "if".
Actions like this serve to placate the public. The general public won't be angry at Microsoft for censoring platforms "known for" or "complacent of" hate speech (or worse). It's always a slippery slope though. Once you open up the can of worms that is censorship you justify future censorship.
I wait to see what will be next on the chopping block.
Edit: A few too many responses to respond to everyone, but if anyone would like to speak with me on it more in depth feel free to email me - information on how to contact me can be found on my profile.