I don't personally understand tributes, but if that's what two consenting adults want to do then more power to them. I also don't mind a compliment and can't help if someone gets excited over a photo I've posted. That said...
As far as "the other thread" goes, it's the surprise nature of it. It's creating a sport out of it, and involving people who may not want to play. It's taking someone else's picture and entering into a competition without their knowledge, and then showing the whole website/the internet how you jizzed on their picture. There's another component to it I believe, regarding sexuality. A straight man is generally less likely to approve of another man cumming all over their photos. They don't want to see that; that's not a gift. Likewise, I'd not appreciate seeing a woman enter my dick into a contest without my knowledge while she fingerblasts herself.