I’m not sure in your specific case; no context, no conclusion. But in most contexts I’d probably do the same as that mod, or at the very least scold the user. Because most of the time, “rent free” is: two types of stupid (ad hominem, assumption), aggravating (it’s often a taunt), and noisy (it doesn’t lead to meaningful discussion). It’s that kind of crap that makes the community less engaging for other members.

@abbotsbury mentioned 4chan; well, that’s one of the things that I’ve seen jannies there removing all the fucking time. (For free.)