No. I just think it's unethical to make money from someone else's work without compensating them.
"But everyone else is doing it" is the kind of reasoning small children use.
"But everyone else is doing it" is the kind of reasoning small children use.
I think the only solution to respect the copyright for this kind of content (amateur content with no identified author) would be to stop publishing it: you can’t sue Tumblr, Facebook, Twitter etc.
Just to be sure: are we talking about the original authors, or the websites who add their watermarks on it?