Oh bullshit. Quit whining about the ghosts in the closet like a child. It's really quite simple. Do you have a rapport with the person in question? If so, you know what they are OK with. If not, perhaps asking them to have sex in the first 5 minutes is a bit forward.
If you don't know how to have a conversation with a person and gague their comfort level, there are in fact courses on this. Take one. Some basics tho: start with a simple, neutral topic. "like the conference?" "great talk! I liked the..." "hi, I'm ... , what is your interest in conference?". If conversation from that point forward is comfortable and easy, feel free to gently escalate. If body language suggests wariness or discomfort or even disinterest, just move on, or suggest talking about it later. You are 50% of that interaction. An interaction needs a 51% or greater consensus to continue. If you take it easy, there would never be problems.
I've been in conversations with women who were obviously uncomfortable with it. Once I spotted it, I politely disengaged and moved on. I have never been accused of harassment. I may have been declared creepy, but whatever the general consensus of my peers is that I am not, so I assume I am not (generally). If some of those discussions I mentioned may have left the woman feeling that way so what? I am not entitled to have anyone think anything else of me but what they do think. Could be I was actually being inappropriate and not realizing it, could just be that the other person was having a bad day, it doesn't matter.
Point being, it isn't that hard to have completely acceptable conversations without any worry about consequence, even if the other person is uncomfortable, so long as you respect that discomfort. Hell, it's even pretty easy to get laid at conferences. In fact, at least in academia, conference sex is a common thing that is openly discussed and joked about in mixed gender company (without resulting in harassment or whatever charges).