Why do girls swear in horror movies?

I am very offended by foul language!!!!!! I can never watch an R-Rated movie whether it is a horror movie especially or a thriller or a comedy that is raunchy because it shocks the heck out of me (instead of the h word that rhymes with bell), I was raised to use proper language and to watch my mouth or I would get my mouth washed down with soap and water. So why is it even right to see horror movies or movies that are disturbing with so many people swearing and having profanity or vulgar?!! This should be illegal!