I think plenty of people who have one nights stands do it because sex is fun and they don't take it as emotionally serious as others do, but I think saying you're jealous of people who have one night stands because they're comfortable with themselves is like saying you're jealous of people who wear revealing clothing, plenty of people do it because they believe it's not a big deal and plenty of people do it because they are uncomfortable with themselves and they want to hear people tell them they're attractive.
I also don't think people who have random sex are all "giving themselves away", but some of them ARE. I mean if you have a one night stand because you want to enjoy yourself and it's not a big deal then that's great and it's probably the right thing to do. But plenty of girls do it because they want to feel attractive or they think it will make a guy fall for them and they probably feel like crap after wards.
I think if you regret having a one night stand, not because of safety reasons but because you feel bad about yourself or because you feel like you gave something away, you were doing it for the wrong reasons, either you didn't want to in the first place or you wanted something out of it (like love or a relationship) which never happened.
At 20, I have friends and aquantainces who have sex with a different person every week, and friends who are saving themselves for marriage. I respect both sets of people, except one girl who would have sex with any guy who had strong emotions for her or any guy who was already in a relationship (including her "friend's" significant others), I don't think she is not self-confident or anything, I think she just doesn't really give a **** about other people's emotions.
I can't say I know too many girls I consider "sluts" or bad people because of their sexual preferences. In fact I can't say I know any. It doesn't friggin affect me who the hell they sleep with and unless it has a really negative effect on them, I don't know why I would form any sort of opinion on that, I might as well form an opinion on who they invite to their birthday dinners or what they eat for lunch.