I don't think either of you have made your point very well. "It's not okay to ... appreciate ... pictures..." Isn't nonsensical, but it doesn't really convey the meaning that I'm assuming was intended (so I guess it's incoherent to some degree). That assumed meaning being that it's not okay to support people that support evil regimes. Even if that support is minimal and indirect.

Would you buy an art book by a Nazi officer in 1942? After all, the officer would only receive a very small portion of the proceeds of the book, in reality providing an infinitesimal benefit to the Nazi party itself. Would you recommend said book to people you know? After all, you wouldn't be providing even that tiny amount of material support. And after all, it's simply the creative work of another human, unrelated to the war or atrocities, not representing the interests of the Nazi party itself.

I'm sure that there are plenty of people that will show up to argue that actually, yes, they would gladly buy the book if they liked it and they would recommend it. And some will have the logical devices to show that there are no moral obligations involved. I disagree. Generally speaking, each of us only have tiny levers to pull, and we should pull them.