Mostly because it's typical von Trier where he takes one of his beautiful paintings and shits on it and says "It's crap." (That's how I explain the bell shot at the end of WAVES, the tex at the end of DANCER, or the end credits of DOGVILLE)
You really have a lot to learn about von Trier and his mise-en-scene. What you say couldn't be further from the truth.
The "Bell shot" at the end of Breaking the Waves has nothing to do with taking something beautiful and saying its "crap". As the film is pitching light and dark religion (as defined by Dreyer) up against eachother, von Trier ends the film with Bess going to heaven and God ringing the bells to signal her arrival, thereby not only saying, that there is a God, but that he is a pretty decent guy, but also that he understands us more than we give him credit.
And there is nothing beautiful about the end credits of Dogville, where von Trier, as the iconoclast he is, pulls no punches in showing us the full extend of the subtext of the film, showing us the true face of the richest country in the world.
In the case of IDIOTS, it's not so much the film itself that's criticized but the whole dogme movement. I liked how von Trier pretty much says the dogme 95 manifesto is a bunch of naive bullshit, like the IDIOTS in his film.
The Idiots is not a critic of Dogme, and von Trier does not say that Dogme is "naive bullshit".
The central element of The Idiots is, it being the second film of his golden heart trilogy, where his heroine remains naively good despite everything. Again, an iconoclast, it, perhaps stronger than any of his other films, convey von Triers idea, that "a film should annoy like a stone in the shoe", that films should be painful to watch, and simplified, the pain will bring catharsis and make the audience react.
In terms of honest emotions, no film of von Trier can match The Idiots. He constantly displays situations deeply humiliating, making us squirm. The essense of the spassing is rebellion, against everything. Sort of emotional anarchy, conformity and rules of conduct are objected. But where the idiots function well amongst themselves, as they all are in on the joke, as they all have defined rules of co-existence, society reacts by their rules. When "society" is unaware of the joke, it is merciful and supportive, when "society" is aware of the joke, it reacts offended. Pulling no punches, Karen is punished with being slapped at the end. For her, the spassing has become a tool of personal freedom, she so desperately desires to be "normal", to belong, that she spasses in front of her family.
And society is an important issue in The Idiots. Free from its restrictions, the group find uninhibited freedom, even allowing the group to openly have sex with eachother. But this is never real. It is all orchistrated by Stoffer. To spass is his idea of rebellion, and either you accept his demagoguery, or you won't be accepted. And that is why spassing fails. What begins as a joke amongst friends, becomes a political manifest in the eyes of Stoffer, and the more political Stoffer becomes, the more normal the groups members become.
To spass is to begin with an outlet, a way to let one go and shake of the frustrations of a conformed society, but it is still a facade, a mask. Just as normal people carry a mask in normal society, so is spass a mask, but with a mirror quality, as those who see the mask, see their own frailty, and thus act as human beings. But it is a too extreme a mask, and that is why the idiots retract to normality.
The Idiots is also a brilliant examination of both satire and tragedy. As long as the spass is unknown to the observer, the idiots imitate people "inferior" to normality, but the moment their spass is realised, their imitation assumes the form of being "superior" (arrogant), and with it, satire is altered to tragedy.
One can, if so inclined, use the metaphore of von Trier to suggest it being about Dogme. Both deal with self imposed rules of uninhibited freedom. But here the parallels end. While Dogme never, according to von Trier, became more than "a little blup" (here making parallels between the nouvelle vague and the blup of Dogme), Dogme was an attempt to shake things up, a provocation, attacking the institutionalised film industry; something which von Trier earlier has attacked directly with Epidemic. There is no demagogism in Dogme, there is no public humiliation in Dogme, there is no blind acceptence of Dogme, as long as you don't get "the joke". To suggest, that The Idiots is a critic of Dogme, is both missing the point of Dogme and missing the point of the film itself.
