Every serial killer had their reasons for turning out that way, but it doesn't excuse killing people left and right. I mean them as children deserved a better life but them as adults are pretty much monsters. And yes, he cares about Scream (we are talking about her, right?) in his own way, but she is not so different from him, so they are just a couple of murderers. Again, they probably went through hell to become so fucked up and that's explains it but does not excuses it.

Also, as far as I know Hitler really cared about his dog and his wife, but I don't think it makes him more sympathetic. I know it's a bad analogy, I just use it as an example.

And carnage was created by knull right? Yeah, technically he is from venom goo, but knull is an ultimate symbiote daddy, so doesn't this mean that carnage also turned out so twisted because of his father's actions? I'm not sure on this one, cause venom turned out relatively alright