I know the thread you mean,and I'm not sure if that person was saying that as a joke or what. But I totally agree with you.
If I didn't have sex out of a relationship then I wouldnt have had sex for the last 3.5 years,and that's not something I'd like to have happened!
Of course sex is meaningful in a relationship and everything. And sex I've had in a relationship can be different to sex outside of one.
I've never had a ONS, I've never slept with someone I've just got off, and I've never slept with someone just the one time. I am reluctant to say the number of people I have slept with, as people on this forum have reacted negatively and called me a slut. I do think this is something that happens on TSR. People who know how many people I've slept with in 'the real world' think its average, and have known people at uni who have slept with way more people.
Sex outside a relationship is absolutely fine (great, even!) so long as both people understand where they stand. I've had a sex buddy for almost 3 years now. We're open about everything, feelings and sex wise, and it's enabled us to do that safely and happily (better sex than when I've been in a relationship. Different of course though.) I'm ashamed to say there was one guy I probably led on a little bit. I didn't know where he stood, and he thought we were more coupled and exclusive than we actually were. Miscommunication, but sex in that instance was bad, very bad.