Incel stuff is pretty much wholly censored on most of the internet, but this forum was created by incels. As much as mainstream society, and in particular the left, despises them, they're not disappearing--if anything, the absolute refusal to openly engage means as a movement they'll probably continue to grow (not that I expect them to ever become fully normalized). Incels believe they have a truth which the "normies" are incapable of perceiving, and that kind of conviction doesn't die easily, especially if everything in their lives appears to confirm it (low status social male, depressed, etc...)--the condemnation acts as further confirmation.
More broadly speaking however, if users want a more mainstream set of voices, this may not be the best part of the internet to be in.
The conflation between men posting about loneliness and isolation, and men posting knowingly misogynistic shit is continuing apace, l see .
Firstly, not sure what "the left" has specifically got to do with it. I get that a portion of those who subscribe to the more extreme incel rhetoric also have an enthusiasm for alt-right gibberish but you don't have to be politically left to find misogyny offensive.
This forum was created by incels, you're correct. However this is not an incel site. Nowhere in the history of the internet has a user of a forum been compelled to subscribe to the views of its creator, however they did also create a separate incel site exclusively for incel content, so fair play to them for catering for everyone.
There is no refusal to engage. Look around any objectionably sexist thread on here and you'll see meaningful attempts made to meet halfway which are responded to with identikit rote-learned victimhood rhetoric. Fwiw there are one or two self-described incels who I've engaged with on here in a meaningful way, who don't do explicit misogyny, with good faith disagreement on this. The issue isn't male loneliness in itself, it's the misogynistic language it's often expressed in. I don't know how often this needs repeating.
The final flourish about "mainstream set of voices" is offensive. This is the ridiculous "the snowflakes are offended" patter of ageing, quasi-edgy stand-up comics that bears no relevance to this website. Suicide is a taboo subject, that in itself renders this forum non-mainstream, but that does not mean boorish and obnoxious misogynistic language should be given added tolerance by extension.
(EDIT) you've added a final sentence there about "cleaning up" SS, this is objectively wrong, outwardly offensive content of any kind will be and should be challenged on here as a matter of course, be they scammers, creeps, manipulative weirdos with numerous alts, fetishists with a suicide kink, all of it. This includes sexist content.