Ugh, the "women only want to date assholes, not Nice Guys like me" schtick. Barf.
I'm just gonna put this out there - confidence. Confidence is the ultimate aphrodisiac. Even if you don't have it, fake it. Save your insecurities until you've got 'em hooked.
Seriously though - insecurity is self-defeating in the worst way. Being confident doesn't mean that you won't get knocked back, but it'll certainly improve your odds. At the end of the day, people are animals - and when you get approached by another human bean, you read their body language. People are lazy - we look for visual cues to evaluate how we should react. If you roll up to a fellow bean with insecure body language/posture/tone of voice, the other person is going to pick up on it. If you don't think you're any good, why should they? If, on the other hand, you roll up with positive body language, you're more likely - not guaranteed, but more likely - to not get shot down immediately. People look to how you act to work out how to treat you.
I mean, look - rejection sucks. But it happens to everyone - even the gorgeous people, believe it or not. It happens to dudes, it happens to gals, it happens to you whether you're gay, straight, bi. It happens if you're rich, if you're poor, if you're genuinely nice or if you're the human equivalent of a headache. It happens if you're good-looking, average, below average - there is not a single person on this earth who has not been rejected numerous times. The only way to avoid rejection is to not enter the dating game at all. If you want to make a genuine connection with someone else on an intimate and meaningful level, you've got to put yourself out there and be vulnerable to having your heart ripped to shreds. It's just the way it is.
In the game of dates, you win or you die.