From what I've heard, a big issue is condoms. Length isn't an issue, girth is. Too large or too small and it rolls up and/or is more likely to tear. Like a too small latex glove, except a dick there's nothing to stop the condom rolling up. Cleaning a toilet and the glove tears? Shit happens. Condom tears? Baby or STD happens. Not funny.
But from what I can tell, a lot of people who post in forums like that are roleplaying having a large dick or gay guys who want to creep on guys with large dicks. People are weird.
The reality is that creeps harassing pregnant women is the least of reddit's problems.
I mean, not so long ago reddit hired a paedophile apologist and IRC diaper play furry fetishist as an admin. They claim they forgot to vet them, but this is the site that tolerated a subreddit with pictures of underage girls for years and gave the mod a custom award.
Expecting reddit to be a safe space for this kind of thing, is like worrying about Epstein stealing beer from the fridge, after you've asked him to baby sit.
Honestly, you might as well burn the whole thing down to the ground. That's the only way to make that site safe for women.
Further reading for those who weren't around or didn't get to hear about it because of censorship on reddit: