>you can still, after all of this, conclude that the piece of art is snobbish, artless garbage.

>I "know" it's worthless to me.

So long as one understands the "to me" is implicit, and so long as one understands that POV to be one of countless POV's, I don't see any issue with criticism.

For myself, if something doesn't work, and I see that it's not the work of a novice, I tend to default to, "It's not for me right now," rather than, "It's garbage." I can still discuss the reasons it doesn't work, but I find this perspective to be more helpful. It makes me more curious about the opinions of people who like it, which gives me more access to more perspectives. When something doesn't work for me, I want to know why it works for others. I don't mean this to come off as a game of semantics.