You know, I have a different view on this. At first, when I found that someone had copied photos from my site, I felt the way you did, but I've reconsidered.
I've got messages from people who are thrilled to find a photo that I have. One person, a quite distant cousin who I'd never even heard of, wrote and said that the photo I had of a woman was his great grandmother and it was the only photo he'd ever seen of her. It gave me a warm feeling that he'd found something so important to him that was just a photo I'd scanned from my mother's collection. (I'd never met that distant relative.)
Later, a cousin that I knew quite well growing up, but hadn't seen in decades contacted me and said he'd found photos of his grandfather on my site. He had no photos of him. I knew this uncle. Saw him frequently while growing up. I was more than happy to share all the photos of that line with my cousin. He now has them on his site.
There have also been people who take the photos, but never contact me.
But you know, they didn't take hard copies of the photos. All the hardcopies are still here in my house in boxes. They weren't "stolen." I'm a teacher, so maybe that gives me a different perspective on sharing information and giving knowledge.
I'm thrilled when I find information on a relative. I copy it to my site (so the reference comes with it). I'm a hobbyist and limited time, so I realize as I get farther back on my tree, that I'm going to have to rely on other people to have done some of the work. If in exchange, they can get a lot of documents and photos from me of more recent relatives, that's a good exchange.
So, I'll keep my tree public.