Facebook is getting on my last fucking nerve

This is something I have never been able to figure out about Facebook: What compels some people to SHARE a friend's personal photos? I don't mean a picture they upload that can be found all over the net. I mean personal photos of their home, their kids, their weekend vacations... I've had my photos of my cats shared on cat pages and my squirrel pics shared on wildlife pages. That's why you'll notice I have my name on some of them. My last account, I had a picture of mine that I took with my cat shared on some guy's wall. Rudeness was bad enough on this site without people exploiting one another's personal photos.