1. You're a woman, and men will hit on you, and that's not a bad thing; it's biology.
2. If you think SF men are aggressive, then obviously you haven't been out much. I don't think I've been anywhere in the world that's LESS aggressive than SF when it comes to dating/mating. Go to Brazil and see what aggressiveness is.
It's a simple rule: if you meet a woman and you're interested in her in that way, then hit on her properly and ask her for her number in a way that makes your intentions non-ambiguous. If you're interested in her professionally then by all means exchange business cards. If you're interested in her in both ways then... well, choose one.
Does a woman not have the right not to face that? If you've got a girl, don't you feel personally that she shouldn't have to face that?
At what point are aggressive come-ons just harassment?
She should have to deal with harrasment? Nope, but that's a different thing entirely. Somebody scoping out your card and then asking you out on a date isn't harassing you. They're asking you on a date. It's what happens after you say 'no' that things become different.
Are you speaking for ALL women?
In Brazil, women love it when you aggressively peruse them.
In SF, men don't talk to women, and women's number one complaint is exactly that.