What is really the motivation for Charlotte Gainsbourg?

Or Lars Von Trier for that matter? I don't think that what she does can be called acting. It's more like autoerotic flagellation or erotic self denigration. She certainly enjoys denigrating herself in every possible way in front of a camera. And you know she's not acting, she is truly suffering all of it.

I guess that the point that I'm trying to make is that, her acting is nowhere near as believable, convincing or realistic as the acting you can see in any other movie by great actresses that now you leave it all on the set and don't take it with you. She is not better than those actresses, she is not more believable than most Golden Age actresses, so what is the point of seeing this hideous troll doing the most disgusting godawful things? Looking the worst she possibly can? To make people squirm on their seats? Fine, you achieved that, but newsflash: making people gag is not art.