I guess, arguendo, different people will have different ideas about what constitutes "art". Art is something like porn was for Supreme Court Justice Potter Stewart: You know it when you see it. This is a definition that doesn't satisfy, and as every good internetizen knows: YMMV. (For what it's worth, if you just put the search words "porn" and "potter" in a search engine now, you will be confronted with pages of Harry Potter porn links. Some of them might conceivably be at least a little artistic, porn and art not being mutually exclusive.) But I think the standard where an image of the red-headed comedian holding aloft a fake-blood-covered Donald Trump mask in an imitation of a beheading falls a bit short of art, and seems a bit more like political porn.
There is a stuffiness about discussing "redeeming social value". Art isn't always redemptive--it can sometimes be cynical and stark as all hell. But points have to be given on the basis of whether a piece effectively conveys what was intended--and I can't say that this does. The "Trump" imagined by Kathy Griffin's pose is, perhaps, a gorgon:
Or a dragon or a giant or a lamia or any other sort of beast that can be beheaded in a legend without our considering that entity as human, but fully monstrous. In a profession where targets are "roasted", audiences are "killed", and failing acts "bomb", this over-the-top symbolism might make sense: It was comedy that killed the beast. (After the tagline of most renditions of King Kong--substituting "comedy" for "beauty". Contra Keats, what is beautiful is not always true, but comedy usually works because of a kernel of truth. Truth, reality, is the anti-matter to a lying regime. But it only works if the joke doesn't need to be bloody explained.)
We don't live in such times where we are dealing with mythological creatures in a way where an audience accepts legend as our referent. Donald Trump is, whatever his faults, a human man, and the worst thing we can say about his policies is that they are centered in dehumanizing others: criminalizing immigrants, privileging some religions over others, encouraging punch-down violence. Where, then, is the sense in dehumanizing him, and making violence a matter of smirking exultation?
It was misguided, and not supported by most liberals, and Griffin herself has now apologized. As a bad bit of art that should be and was rubbished, that should be that. And yet we now have a counter-example to whatever violent image fuckery we on the left mean to decry-- "But Kathy Griffin". This is absurd, and completely expected.
It should not take the sting out of factual claims about what is happening on the right, however. The gorgon's head was never meant to shock us liberals, you know. Attention-sponge and thirsty-comedian Kathy Griffin was pushing RW buttons. And I would be afraid to wade in into her social media mentions right now, because that woman is probably getting cause to call the authorities--and that? Is as well worth talking about as her satire-misfire. I believe she intended no threat (does anyone seriously think even a D-list celeb is going to be a fence-jumper?) and is probably just being nearly Ted Nugent-levels of shit-talking stupid.
But if you come to "But Kathy Griffin" at me, I will "but BLM" forever. Or "but queer-bashing" forever. Or "but Portland" forever. Because a ham-fisted visual message isn't the same thing as actual physical violence, any more than eating a menu is just as good as eating a sandwich. And while Griffin's message was botched, she wasn't actually trying to get anyone killed.