I think I'm going to use Meredith's approach (see the comment above you) and make an explanatory entry covering as many of these issues as I can, in a sort of Q & A format. That seems gentle and appropriate. There are a LOT of kids on DA who aspire to be professional artists. Heck...I wish there had been a DA for me when I was a kid; I would have LOVED it. However, if I don't speak up and make them aware that plagiarism is wrong & unacceptable & NOT really "art", then they'll just keep doing it. And then I've done no favors for all the other artists who get their work swiped online...you know?

As for the anxiety thing...it'll pass. It always does. :-/