Both are all about perception rather than substance. In both, the medium defines the message, the package defines -- or obsoletes -- the content.
How many doctrinaire conservatives do you know? What use is "art" made of feces?
You make an interesting point.
Conservatives will tell you that there are absolutes in the world: is means is , for instance.
Liberals like to change the rules as they go, so that they never have to take responsibility for anything.
"Modern art" plays on the liberal insecurities and lack of absolutes perfectly.
I've made my living as a designer and artist, and frankly, I have no use for 'modern art'.