I think you and I have different meanings in mind for the phrase "hit on". If I'm at a conference and meet a woman I'm attracted to (and likely has similar interests since she's there too), why would it be bad to try to get her phone number? I may never see her ever again.

Below you talk about "not taking no for an answer". I don't call that "hitting on", I call that pestering and, yes, that would make someone a dick. But in my opinion that makes you a dick no matter where you do it, not just in business scenarios.

You should be ejected from a conference for hitting on a woman? I think not.

Are you at a conference in order to expand your professional network and to learn, or are you there to be a sleazebag?

Why can't you expand both your professional AND personal networks at a conference? Hitting on someone doesn't necessarily make you a sleazebag-- there are respectful ways to do it.

When you do it repeatedly and refuse to take no for an answer (like the jerk in my anecdote) that's the problem. Also realize that every woman at a conference gets hit on by about 20% of the men she talks with. At the last conference I attended our marketing coordinator decided to draw a penis on every business card given to her by a guy who hit on her. Out of something like 200 cards, 39 were sorted out into the penis pile.

When you hit on a woman while she's working, you're not going to get laid, you're just going to be the latest in a long string of men making her life hell that day.