The only necessary explanation is that people don’t want or like the content. There is a ton of NSFW material on Lemmy that exists plenty peacefully.

The issue is that the (low effort, low quality) content is hard to block because of the constant pivot to new communities and accounts. I don’t want to see it, but I could simply block it and be done with it if they’d keep it contained to a single place. Since they’re being SUPER annoying about that though, it gets downvoted. It’s bad form on that user’s part.

I didn't downvote the one post I've seen (like you and others said, to each their own), but I recognized the style from the subreddit and felt negatively about it. Doesn't have to be sabotage. Could just be people who remember the beforetimes metaphorically recoiling.