Because any tool will be eventually misused and abused.
You don't need tools to kick nazis off your platform. And who cares what homophobes do on their platforms? Don't use them.
Like for example in this case the Mozilla Acceptable Use Policy. Change a few words, add some statements, and it can be used against Antifa.
Homophobes were just an example, you can substitute with Nazis or others.
So yes, the whole point of Antifa is already unacceptable by that policy.