This is a dangerous short term move. In the end it may create a division and popularize other social medias where this content and worse will still be available in an unmoderated space.
The problem with Facebook and Twitter is that everybody is on Facebook and Twitter. Some alternative comes up (let's call it Foo) that lets Trump speak freely. How many Facebook people are going to move to Foo to hear Trump? (Remember that the value of a social network is proportional to the square of the number of people there, and nobody's on Foo yet.) Sure, some will go, and Foo becomes a nest of die-hard Trump supporters. And over there, they get worse, more hardened in their position. They also don't get many new converts, because if you're not already a hard-core Trump supporter, why on earth would you go to Foo?
Is that better or worse than the current situation? I think it's better, because it shuts down the recruitment pipeline.