Here's my take as a cat (and dog) owner.
First, I don't think posting photos of cats here will attract this lunatic cat killer. These attacks have taken place over a huge area. If anything, knowing locals are keeping an eye on local felines would be a deterrent.
Second, I'll admit I felt the same when I first saw this thread - it seemed rather impudent to take pictures of other people's pets and post them here. But for the life of me I can't rationalise that reaction. It's not logical. And if I found a picture of mine here I'd be flattered rather than offended.
The argument that people who don't know about the forum might be upset to know their pet's picture is on it is self-defeating. If you don't know, you can't be upset by it.
This is HUGELY different from taking picture of people's children.