I too think it is a bit one sided, but with a man things are far more sexually explicit as their parts are more obvious. I think may women (and maybe men) would be uncomfortable with a fully naked male frontal. With a woman, it is more acceptable as it has been commonplace.
I don’t watch sexually explicit films [although I do like “Sleeping With The Enemy”, “Pretty Woman” and other lighter sexual films] but can understand the allure. Men’s parts are more obvious, but nude women are also graphic. As long as the film is with friends and NOT my father or sister, I am fine with it. If you’re easily embarrassed about watching that kind of material with family, check out the certificate of it! And do also realize “Black Swan” has a woman touching herself [fine, nothing wrong with that] so, again, if you’re easily embarrassed, don’t watch that film with family!