Porno flick, hard 'R', NG 18, or something else, what would existing movies be if the sex scenes were graphic?

If you have a movie like 9½ weeks, The Lover, Looking for Mr. Goodbar, Eyes Wide Shut, Basic Instinct, The Accused, etc that showed all the sex scene in graphic in and out clear detail would it be considered a porno flick, even though most of the film did not involve around the sex scenes? And why if it did it would take a film (some critically acclaimed) and turn it to the dark side?