As women get older they realize that even though a dude is with them, they are still turned other women, even some not as hot as them. Guys should know the same about their women too.
As heatherrae said - in most cases it's just jealousy. Some women are genuinely revolted by it though. I could never go out with/date a woman who wasn't sexually open enough to watch porn or to 'let me watch it'.
thats because 80% of them have their own porn sites or web-cams pay per view...( they use the dating sites for free promo's) the fat ones are waaayyyy into porn....so yeah, i WAS looking at the 2% at the time...i gave up tho. cause by the time i met one of the 2% for a date they had gained 20lbs.