I promise not to kill them just because you shared the theory. Boy Scouts honor, I will even write them on my 'safe' list under Edward Nigma.
Oh that's only one group, I'm sure some kill..somewhere, I haven't met them, but I find no reason to. Why go against someone who will actively try to murder you? I get enough of that from my friends and associates, much easier to go nice and safe, a punch in a face, a few broken ribs, maybe a broken back, but at least I get free healthcare at Arkham.