What is the true of humanity?

"How many zombies you kill?"
"How many people you kill?"
"Why?"

These are the question that will be asked when Rick met a stranger.
It seems simply questions, but it all  matters.
To survive in this world full of zombies wandering around, does humanity still works?

Some survivors had abandoned their humanity: they build up a camp at the terminus, called it "Sanctuary". It sounds nice, right? So all people will gather to the camp, and feel like safe, protected and settle down. But what they truly want was to maintain their food supply by killing all the incomers, and get their meat.

Seriously, do they really have to do this?! This is never humanity!!!

The group which all the main characters were inside the camp, all of them was nearly dead. They were so lucky to escape, but since that, I feel that the humanity of them was getting away from them, even Glenn said that humanity is what they left.

Humanity is what keep us human, act like human. All what we do will have a limit, a line that we can't go across. If we went across it, we are not human anymore but an animal.

But this part about humanity just for the action-reaction between humans and humans.
So, for all animals and other living thing even the environment itself, does humanity still exist in us?