So then why do promiscuous, commitment-avoiding studs still exist? If it weren't a viable reproduction strategy, any such disposition to this behavior would have been bred out of humanity through natural selection and we would be perfectly monogamous. Obviously that's not the case, so being a promiscuous male must be at least a somewhat successful strategy.

I don't want to get into a treatise here -- especially on material I'm far from expert in -- but you may want to check out some texts on evolutionary biology. A good primer is called (for real) Sperm Wars, by Robin Baker. It's a pretty eye-opening look at the evolutionary theory behind human behavior. I'm not saying it's got all the answers, but he makes a lot of compelling arguments.

Warning: If you're a hopeless romantic, you probably won't like it, and you might even violently disagree with the conclusions he draws, many of which are not flattering to the idea of monogamy.