>It is a monumentally difficult task to create a forum these days, from a social PoV.

and legal, and probably technical PoV as well; yes.

The large platforms have sucked all of the oxygen out of the room, and have gained what I feel is an unhealthy control of what can and cannot be said.

I have no idea what can be done to fix the situation; but none the less, there it is.

From a technical perspective, forum software is easy enough to use.

A technical perspective also includes mitigating denial of service attacks and other security issues, including scaling.