That's one of the biggest problems with sarcasm/irony in casual writing. There's always someone who misunderstands and treats it as serious. This problem is amplified by the number of eyes a typical internet comment receives. It's a major way people are radicalized by internet communities. There's always a proportion of members who are being "ironically" sexist/racist/discriminatory but eventually people take it seriously, the ironic commenters are pushed out of the community and presto, you have 4chan and worse.
I watched this happen in /r/TumblrInAction. Over the years it got more mean spirited and fell for more obvious trolls/satire as people less committed to the cause of disrespecting self-identity moved on. Now it's all "lol attack helicopters" and cruelty, and half the former regulars are now queer leftist furries.
I loath the cheap humor aspect to forum commentary. It is hurtful as noise or incidentally inflammatory, as you mentioned. There is no way to eliminate it, but that isnt the point. I dont promote pure misdirection.
