1. The question, "Is it art?," is passionately debated because both sides assume that art as such is valuable, that if a thing is a work of art then it has a place in a gallery or museum, that they all have something important to say to and about the culture.
This, I think, explains why people (like me) who, frankly, don't know very much about art, will get involved in these conversations, where they wouldn't if the question were, say, "Is it engineering?" If the assumption that art as such is valuable is true, then to concede that a signed urinal is "art" is to give it an irrevocable place at the table (as it were).
2. It seems to me, though, that the above assumption is false. Art as such is not valuable. We can say "both"/"and." That urinal is art, and it should be chucked into the nearest dumpster.
Recognizing that art as such is not valuable makes the question, "Is it art?" a lot less interesting to the general public, with two immediate consequences. First, it allows artists and their critics room to create and discuss art without constantly having to defend themselves from attacks from people who don't know much about art but know what they hate. Second, it prevents the culture from being held hostage to jackwagons who put their own feces in tin cans. They can go right ahead making crap, and critics can go right ahead talking about how artistic their crap is, and everyone else can laugh at them.
Granted, acknowledging that something can be both a work of art and worthless doesn't resolve all the tensions between art and society. We still need a way to promote art that serves the common good and demote art that does not. But we can at least cut the legs out from under the claim, "This is art, so we must respect it/fund it/make it public."