I understand your point, however, the Piss Christ photo, is in fact an award winning piece of modern art.
http://en.wikipedia.org/wiki/Piss_Christ
A jar of piss with a crucifix may not be art, however, photographing it and displaying the photo as art sets it apart from just "urinating on something holy."
Can you not read deeper into the piece past the piss and the christ?
It's a statement, not just urination. therefore, it is art, and that's why it was recognized as a great modern photograph.
I have stood before Picasso's Guernica, I have coordinated Andy Warhol, jeff Koons, keith haring pop art exhibits... need i remind you of who Jeff Koons is and what he "passed as art" in a gallery setting?
Jeff Koons took pictures of himself having sex, including close up cumshots and vaginal penetration..
art is art and no one can DEFINE it.
http://en.wikipedia.org/wiki/Jeff_Koons