Nudity is not necessarily pornography. Vulgar depictions of human sexuality is.
What I think most people are upset about and which is very destructive of our culture is acts relating to sex which have traditionally been defined as "obscene."
I don't have any problem with making depictions of these acts illegal using a national, rather than community, standards.
And obscenity is not, nor has it ever been, protected by the First Amendment.
There are several artists who could be the "world's greatest artists" you cite and I seriously doubt they would paint women the same way Larry Flint would pose them.