The apprehension people feel about killing others is a fairly universal thing that I don't believe to a purely social construct like "morals" (whatever that is).
I am fairly comfortable labeling "doesn't mind killing people" as sufficiently abnormal to be called "ill".
You're not correctly quoting the parent comment (I'm not sure you're quoting anyone, it looks like you're erecting a strawman), he said "willing to kill".
There is a lot of ground between being willing to kill, for example to save the lives of others, and not minding killing.
The apprehension people feel about killing others is a fairly universal thing that I don't believe to a purely social construct like "morals" (whatever that is).
Well, once you've thrown away morals, it's true that all you have left is the hope that others will refrain from killing others due to not feeling like it.
Morality is just the portion of goals that humans in a given culture share, but I'm not sure you should be so quick to dismiss it as a positive force.
I think what we call "morality" probably has a biological basis as well. Humans are social animals. Hence, we're going to have selection pressures towards behaviors (and the internal thinking required to produce those behaviors) that preserve social groups. If we didn't, human groups wouldn't survive, and we wouldn't be social animals. I think we can point to other social animals as examples. There's also support in the fact that there are broad similarities across cultures about what is moral - for example, murder is wrong. If there was no biological basis, I think we'd see far more variation in what we call "morals."
What would make you think so?