Men can sleep around without ill effect? Tell that to my chlamydia infection. Ba-da-bing!

Seriously though, your observation is totally cultural and most certainly doesn't apply in the Bay Area. There's no real stigma against casual sex here and since there is a 10:1 male to female ratio, the women are totally in control. Women here have the luxury of figuring out exactly what combination of dick size, personality, paycheck and hairdo they like. The men, rather than being predatory cads, are reduced to fretting over whether or not they should get a tattoo or an $80 t-shirt in hopes of maybe possibly (probably not) attracting the attention of a google PM.