Men love it when women approach them. Men who don't like confident women are insecure themselves.
That being said, our society still has a problem seeing women as aggressive, sexual beings. Many men see aggresive women as simply easy. That's unfortunate and a result of the double standard we have. A man who sleeps with many women is a hero, while a woman who sleeps with many men is a whore.
My response to that is.."If you really love her, it doesn't matter who she's slept with before, just be happy she's sleeping with you now."
(as long as she doesn't have an STD or is cheating )