Consider conferences like your office. Sure you can hit on a woman, free speech is a right, but you're also a dick for doing so, and should be ejected from the conference, or the office when your employer finds out.
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.
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.