Salo is impossible to find. Long out of print. If you can't depict the horrible in films can you do it on stage? In music? In novels? Why should film be treated differently from other artforms?
If "the horrible" is being depicted so some sick guy can use it as wank-fodder, then it sinks to the level of porn. Most of the Salo fans I know of are gay guys for whom scenes of people being forced to eat feces are considered entertainmant. Likewise, kiddie-porn fans are going to love this new Dakota Fanning movie.
The point I was making about earlier about the defenders of Salo is that we really don't need a movie to explain to us that rape, murder, and torture are really, really bad. there is enought archival footage and eyewitness testimony of the atrocities of WW2 to make that point clear. If that's the only reason for filming horrible things as entertainment, then it is a weak one, IMO.
Likewise, dramatizing child-rape is showing us that somehing is bad when we already know it to be so. The word "art" gets used pretty loosely these days. I suppose you could call a hip-hopper who extols the virtues of gang-rape and murder an artist, but I would not.