Most comics are not truly rebellious or creatively free. Most comics, paintings, music, etc., are derivative of other, more successful works. And it's quite often that those without much rebellious spirit are the ones to imitate it. Genuine radical expression is hard to come by, but it usually crops up when money is not a motivating factor. You can take all the liberties you want when someone else's dime is not at stake. The validation is not a threat to comics. A far greater threat to the creative freedom of artists working in any medium is self-consciousness and self-censorship.