That is the idea definitely. It mostly works too, just like you said it's a diverse group of subcommunities all with their own rules. But they found that free speech platform wide meant some truly nefarious subcommunities could exist on their infrastructure, these subcommunities didn't self regulate enough. Quite reasonably they have decided they don't want that to happen and have stepped up the platform wide censorship.

The contention seems to be where they draw the line, and just how free their version of free is.