We don't have to justify liking larger cocks any more than we have to justify any preference, large cocks are just one of the qualities we'd like in our ideal man. We offer in return what any woman would hopefully offer, an amusing, warm, very sexual dalliance/relationship/whatever. You seem to be assuming that relationships are tit for tat, he offers something, I offer something and all things have to be equal and also that a big cock is some prize that deserves something in return, it's just a fluke if a guy has a big cock and unless he bought a lot of other things to the table he wouldn't be deserving of much of anything. You get out of a relationship what you put into it.