I agree with kawecki and Gaby. In the last few years it seems my country ( USA ) has descended into a new era of McCarthyism. Free speech, in all its forms, is withering under such a never ending barrage of politically motivated assaults by fanatic special interest  groups that it is in danger of disappearing altogether.
People are actually being jailed, harassed or driven into bankruptcy for saying, writng, or graphically representing an idea that somebody somewhere claims to find offensive. In my own home town, an eighteen year old severely mentally retarded boy was arrested and jailed for uttering a racial epithet in the presence of some minority students while they were boarding a bus. This child has the I.Q. of a five year old, and had no idea the word he used was in bad taste. He was just repeating a term he'd picked up from a movie or an overheard conversation. But that didn't stop the local "justice" system from putting him in handcuffs and locking him in a jail cell when a complaint was lodged. Because his parents are poor and could not afford to hire a lawyer or post bond, the boy spent several days held prisoner in an unfamiliar, hostile, frightening world he could not understand. Thanks to public outcry the charges were eventually dropped, but I wonder what would have happened if no one had protested this outrage?
Those who own and control the Renderosity site have every right to regulate the content that appears in the medium they pay for. This is not a publicly owned resource, but an asset of a financial enterprise. But does having the ability and legal right to enforce a policy justify its use? In this instance, I do not believe it does. After all, we are dealing here with graphic artistic representations, not reality itself.