Resteems are great for displaying the artists original work, but what if your post is a spotlight 'this is the top ten pictures of "x" on Steem this week'? In that example, you'll probably get a reply fairly quickly from the original artists, but if it weren't a post about steem art how long will they leave you hanging? Is their art no longer deserving of being included just because they're a prick that week? Maybe they were sick.
My point is that there are community guidelines and unspoken rules of thumb that create a grey area. Strictly adhering to US copyright law on an international community is incredibly short sighted, and the community needs some custom guidelines.
I'm sure we'll get there.