They might have the courage, but do they have the judgement to decide who's an actual neo-nazi?

Twitter has a history of political partisanship. They'll ban "racist" conservatives but allow minority "terrorist" organizations.

There's a Pacific Ocean-sized gulf between the current policy and your nightmare scenario.

Slippery slope and all that, but they un-suspended Richard Spencer for "reasons".

After the neo-nazis, who's next? As soon as they "take sides" they are now directly putting a finger on the scale of national and international politics. That's a rathole they absolutely do not want to go down and would very likely be totally unsustainable.

On the other hand, it works pretty well for the Chinese social media.

It's not a nightmare scenario, they literally let terrorists use the platform no problem