No problem with it whatsoever. I think it's often much more honest. Just because I'm sexually attracted to someone doesn't mean I'm emotionally attracted to them. It's rare I get emotionally attached to a girl enough to really consider my feelings romantic, but that doesn't mean there isn't sexual tension, better to just let it out, I think. These things tend to fester, left to their own devices.
Even if I thought it WAS bad idea, how the hell is what people do with their time any of my business?. People make mistakes, it's part of life, and trying to prevent them will just lead to different ones, all we can do is allow people freedom enough to grow wiser.
And would I date a woman who slept around beforehand?, why not, I'd do it to and it's not hurting anyone. Why would I be upset that the person I plan on having sex with is experienced in sex?, like it's left some kind of evil residue on her(Before anyone mentions STD's, I wouldn't sleep with anyone I didn't know well enough to trust not to give me aids, and I'd use protection anyways). The obsession with chastity is from an age when people would regularly sell their 12 year old's to their brothers. There's no real benefit in practicing it, and there's no real harm in not practicing it. Hell, I'd say that being sexually reserved is actually more problematic then being sexually outgoing.