this is art and shouldn't be fucked with unless the director wants to do it himself.
I disagree with this.
1) The "art" can often be adulterated one way or the other. The studio declares the rating they want and the director may have to cut or otherwise edit things to hit that rating. This sacred nature of art doesn't seem to factor in when this is an issue. On top of this, as stated, there are edits already made for regular TV network broadcast. That such editing is OK and it is not OK when the studio decides to do it for sale makes no sense.
2) Hiding behind that idea of art is a pretty thin veneer. Take a good look at the films in the theater- are we really making the argument that War for Planet of the Apes, Spider Man Homecoming, Despicable Me 3, and Baby Driver (this weekend's four top grossing movies) are making deep statements as they explore the human condition? Ha. Nowadays the movies that really are works of art are greatly outnumbered by mediocre fan service, transparent money grabs, and other types of movies that nobody is going to mistake for something on the order of Casablanca. Yes, art is subjective, but the notion that it's sacred and should not be fiddled with a pretty thin argument for me. It's entirely a matter of opinion. Art is constantly taken, fiddled with, and reinterpreted by others. Which leads me to...
3) Nothing is affecting the original. We're not talking about painting a mustache on the Mona Lisa. We're not chiseling boxer shorts of Michelangelo's David. Nobody is gathering up every copy of the White Album in existence and replacing it with something else. It's a copy. The original stands alone and can be distributed right alongside the edited one. Cutting the dangling blue schlong from one edition of The Watchmen would do absolutely nothing to those who still want to see cobalt colored man meat and choose to purchase the original. There's no actual harm suffered.
IMO, this is a matter for the holder of the rights to the media to decide. If a studio holds the rights and wants to do it, fine. If a director wants to be a stickler and negotiates the ability to refuse such things from ever happening, fine. But I don't think there's any legitimate reason to bar anyone from editing a film or anything else up or down in rating for a commercial release so long as they hold the appropriate rights to the material.