I know people it works really well for. And for it to work, they need to be the reverse of desperate, because they need to be happy with the rest of their lives. They need not to want the disruption and compromise of a relationship at that stage, but to enjoy the physical side of sex, and to want it without it in an emotional context that's making massive demands on them. And mostly, they have kids, and don't want to inflict the potential stress of a step-parent and/or step-sibling(s) on them while they're kids. But they enjoy sex, and enjoy it with someone they happen to like and trust.
I don't think any form of consensual sex is tacky, and I think that comes from the traditional perspective that women had to lodge their worth as a person on how wary they were of allowing access to their vaginas, and that if they weren't suitably reluctant, they were themselves tacky, or worse. But true casual sex is a total gamble, because mostly, sex with someone you don't know well is a bit crap; they don't know what you like and vice versa. Good sex, in my experience, always took time.
I think needy sex, or exploitative sex, is sad and disgusting respectively. But a true FWB arrangement is neither of those things, is it?
I mean, I've been with my husband almost 20 years now, and we're monogamous. But that doesn't mean everyone else should be. I just don't understand the need to append value judgements to what other people choose to do sexually. With a FWB nobody is faking commitment while running around shagging behind backs.
I do agree that it's dangerous, though, because so often feelings will develop and someone will get hurt. It only seems to work when neither party wants that, and that, as I say, seems to work best when the woman is a single parent. Or maybe it's just that those are the two cases I know of where it has? Anecdote not being data, and all that, it could just be that the people I know tend to be at similar life stages with kids.
Meh. Life is painful, and chances at happiness should be taken when found. All relationships hurt us at some stage, even if it's ended by widowhood. Whatever gives people some joy is a good thing, no?