Sin based on imagined thoughts sounds way too Orwellian to me. Scary, in fact. As someone said, "Our minds are our last bastion of privacy." Penalizing thoughts? Count me out. 

Your framing would make fantasy a sin. And it even would make literary or film  fiction about sin a sin in itself.

 You are 100% right--objectifying women is wrong. But would you call it a sin to DREAM about a woman? You'd have to get rid of a lot of poetry and love songs, from "I Dream of Jeanie" to "The Last Thing I Think about at Night..."

You use a term I have seen on this site (it's always about sex): "selfish pleasure." When is sensual pleasure UNselfish? 

I've appreciated your responses.