The thread is a bit contradictory. The title is, "how do you like your sex?" The poll is called "sex before marriage". And the thread question is, "Should the young folks go for it or hold back till marriage and it's too late to run screaming for the hills."
Those are very different questions. What I like for my sex is not identical to what I think other people should or should not do.
For me, I voted not married, but must be in love. This is because that's what works for me. Marriage doesn't mean anything to me, and I philosophically oppose the concept. But for me, I have zero desire to have sex with someone I'm not in love with, or to have sex with more than one person. For me, sex is more than just physical; I can only do it with a deep emotional connection. So I picked "not married, but must be in love".
For others, I don't care how they have sex as long as it's between consenting people of rational age. I don't view it as an ethical or moral thing. The only factors I consider are what people desire, and what is healthiest for them. If people want to have sex with multiple partners, or sex with people they have a friendly agreement with, I think that's totally ok. As for one-night stands, I don't think there are any ethical issues, but I don't see how the risk/reward ratio is a good one for having sex with someone you just met that day. It seems smart to me to at least know the person as an acquaintance first, but whatever.