I haven't used 99Designs. I suspect the artists who object don't consider people who use AI to be artists. I have to admit, I struggle with that concept, because if they were *real artists*, you might think they could create their own drawings from scratch, and not need to copy other people's work in order to get a picture of a dragon. Although there's a difference between copying and inspiration. I can guarantee that if I tried to draw a dragon and used an image of a dragon for inspiration, my drawing would probably bear little resemblance to the dragon pic that inspired me, because I'm not very good at drawing!
It's all very murky. I've now come across two lawsuits over AI art. One being filed by Getty Images and one by three photographers whose work was ripped off without payment. I will write about them.
Did you see this story about AI images and copyright? https://medium.com/illumination/images-created-by-ai-arent-necessarily-copyright-free-5b846459a5ac