In this area I find the writings of Eliezer Yudkowsky particularly insightful. Definitions are what he calls "disguised queries." When someone says "atheism is a religion" or "that's not art," they're trying to use the definition to make another statement - that atheists rely on faith, or that the work is not worthy of praise, display, etc.
The problem is that set membership isn't always binary, and not all members of a set share all the same characteristics. Just because something isn't difficult technically, doesn't mean it's not art. More importantly, if you're using "not art" to mean "not difficult technically," then saying "this isn't difficult technically, so it's not art" isn't a worthwhile statement. It's the disguised implications of the word "art" which make such statements so contentious. To paraphrase Eliezer, the argument about what is and isn't art is really a dispute over whether to infer art-related qualities of the work, like fitness for a museum. A dictionary is of no use here.
The problem is that set membership isn't always binary, and not all members of a set share all the same characteristics. Just because something isn't difficult technically, doesn't mean it's not art. More importantly, if you're using "not art" to mean "not difficult technically," then saying "this isn't difficult technically, so it's not art" isn't a worthwhile statement. It's the disguised implications of the word "art" which make such statements so contentious. To paraphrase Eliezer, the argument about what is and isn't art is really a dispute over whether to infer art-related qualities of the work, like fitness for a museum. A dictionary is of no use here.
http://lesswrong.com/lw/nm/disguised_queries/