You're going to find where someone has been victimized in this manner before, that they will most likely be AGAINST any such an option. I'm not a writer, so I've not suffered plagiarism of my written stuff; but I have been victimized on the art end. Not pleasant, and yes, still testy about it. Like most artists, I'll share my stuff, if asked. Was I asked? Nope.
I'm glad we don't offer that as an option, personally. If it helps even in a small way to prevent someone's work being lifted, it's worth it to NOT allow downloads.