I have heard a lot of men who feel like you do. Something they fantasize but highly unlikely something they would every do in RL. I think you should ask your woman about this, because it will always nag at you and it would be the outlet you need without landing in prison. I think for men, the fantasies come from testosterone and cave man genes predominetly. Long before the internet, men have felt this way. Even the average" nice" guy has them.
I read a really interesting story was the daughter of Cher who had a sex change to become a man. She/he went from the name Lisa to the name Chase. She/he said that when he started hormone shots (testosterone) he started thinking about sex A LOT more than he ever had before. And he felt he became slightly more aggressive/assertive in general. I've heard it be said that men think about sex every 10 seconds (or something like that). I used to scoff at that but after reading Chase's story, it opened my eyes to why guys behave the way they do. I honestly feel bad for them in the respect of how incredibly annoying and disruptive it would be to having your mind be constantly dragged back to thinking about sex, especially if you are really trying to concentrate on a project or idea, etc.
I agree with you as far as the "caveman" genes. For thousands of years the men more likely to survive AND pass on their genes were the stronger and more aggressive types. In a primitive society brains don't count for much - muscle and violence do.
Primitive human societies are a lot like animal herds/packs. The "Alpha Male" of a given group has more chance to breed - he is the most desired by the females. Many animals fight for the right to
party I mean reproduce: defeating other males in physical combat proves superiority and guarantees mating privileges. Consequently the Alpha Male passes on his genes - and the next generation continues the cycle. primitive human societies aren't/weren't much different: a strong warrior or man of wealth and influence who was a good provider could have several wives - or (if polygamy was not permitted), have his pick of the available women since nearly all would be happy to have him.
You might argue that modern society is not like that. Well it's not quite as brutal - but the same general approach applies. Women are still attracted to Alphas - sporting champions, movie stars, influencial politicians - or men who are just plain rich. The successful male has more breeding opportunities - for basically the same reasons. Women are biologically programmed to desire men who are strong/successful/good providers because those men have the greatest chance of providing for their children. To put it simply, I believe human society has advanced a lot faster than human evolution. So while we have the morals and values of civilised people we still have the basic urges of our caveman ancestors.