It really does come down to context, and the perspective of the viewer. I have no education in dance, and watching it and appreciating it for me is very much an outsider's viewpoint. I can appreciate dances that include feats of physical strength and skill, but other more "conceptual" dance just looks to me like people wiggling their elbows. Because I've had these discussions ("Is this art?") so many times throughout my education, I understand that there's a huge amount of fundamental information I'm missing to "appreciate" the pieces that go over my head.
It's the same with people who argue (one way or another) that representational painting is "good art" and abstract is "bad." They are lacking the foundation to understand why others might say the opposite, or that both are equally "good."
And frankly, that's ok. If we were all on the same page, how boring would that be? If that were the case, modernism wouldn't even exist, as it really began as a rejection of the academic system of art.
In the end, I usually fall back on John Cleese's line in the Monty Python Last Supper sketch; "I may not know much about art, but I know what I like."