Not only is it kind of rude, like whistling and hollering, but I just don't know what these guys think they are going to accomplish (same with whistling and hollering really)

Evo psych has a plausible story to tell. There's pretty good evidence that women find perceived "high-quality" males more attractive during their fertile periods, presumably tied to a tendency to head off secretly for a liaison to get better genes while their regular mate still helps raise the kids. In that environment, signalling the woman that you've noticed and would be willing would be a significant adaptive edge.

Of course we are far more than such tendencies and have both the ability and duty to overcome them to be decent, civilized people. But on the other hand I don't think men should feel they are bad people if they notice some inclination to do those things.

We pedophiles are a hiccup in nature, just like gay men. But whatever made us attracted to young girls, it's not surprising if some inclination to wolf whistle comes along with it -- if it can be done without someone beating you up, and web anonymity provides that.