Reddit is not a public utility or a public square; it’s a privately owned space on the Internet. From a legal and (United States) constitutional point of view, people who post on Reddit have no ‘free speech’ privileges; they have what speech privileges Reddit itself chooses to provide them, and to tolerate. Reddit chooses to tolerate creepiness and general obnoxiousness for reasons of its own, in other words, and not because there’s a legal or constitutional reason for it.
Personally speaking, when everything is boiled down to the marrow, I think the reason Reddit tolerates the creepy forums has to do with money more than anything else. Reddit allows all those creepy subreddits because its business model is built on memberships and visits, and the dudes who visit these subreddits are almost certainly enthusiastic members and visitors. This is a perfectly valid reason, in the sense of ‘valid’ meaning ‘allowing people to be creepy isn’t inherently illegal, and we make money because of it, so we’ll let it happen.’ But while it makes sense that the folks at Reddit are either actively or passively allowing ‘we’re making money allowing creeps to get their creep on’ to be muddled with ‘we’re standing up for the principles of free speech,’ it doesn’t mean anyone else needs be confused by this.
If someone bleats to you about any of this being a ‘free speech’ issue, you can safely mark them as either ignorant or pernicious — probably ignorant, as the understanding of what ‘free speech’ means in a constitutional sense here in the US is, shall we say, highly constrained in the general population. Additionally and independently, the sort of person who who says ‘free speech’ when they mean ‘I like doing creepy things to other people without their consent and you can’t stop me so fuck you ha ha ha ha’ is pretty clearly a mouth-breathing asshole who in the larger moral landscape deserves a bat across the bridge of the nose and probably knows it. Which is why — unsurprisingly — so many of them choose to be anonymous and/or use pseudonyms on Reddit while they get their creep on.