In both cases there is a complex interplay. Violent media can normalize violence and can cause people to be more violent (at least short term). It can also have no effect at all. It depends a lot on the content, the environment and the person.

Nudity can lead to sex, but it can also contribute to sexual education (which reduces teen pregnancy and STD risk). It can also change you body image in negative or positive ways. It depends a lot on the content, the environment and the person.

In any case, America's war on the nipple is in no proportion to the risks.