Facebook itself isn't a cesspool of just 1 side, so isn't meaningfully associated with any one. Independent and overlapping cesspools of all strokes form and grow in multitudes there.
This statement is incorrect. Twitter has a huge harassment problem, that users have been begging the company to fix for years, to no avail. There are users openly associating with nazi ideology (not exaggerating here - we are talking about users with swastikas as their avatars, nazi references in their bios, etc.[0]) harassing others on the platform. In no way is this people in their little bubble, being perfectly isolated from others who don't share their ideology.
As far as left-wing vs right-wing or whatever, I don't really care. I chose nazis as the main example because this is a very clear ideological group that has been unequivocally responsible for crimes against humanity in the past, against which Twitter chooses to do absolutely nothing (even if this contradicts their own TOS). Well, they choose to do one thing: make those accounts invisible in countries where they would be breaking the law if they didn't. So they literally have a `isNazi` flag in their database, but they only choose to use it to not get in trouble with German/Austrian/etc. law instead of, you know, just banning people who are calling for ethnic cleansing. Great job, Jack Dorsey.
If there are other similar ideologies (left wing, right wing, or other) you would like to put in the same bucket, please do - I have no issues with that. The only fundamental issue is that Twitter is choosing to let extremist, well defined, communities such as nazi ideologues thrive on their platform because growth or something.
[0]: if you really need proof: https://twitter.com/anp14
This is what Twitter and Facebook are today (Twitter will even hide these accounts in their German digital coffee shop, where spreading Nazi propaganda is illegal, but are fine letting it be for the rest of the world).