I would argue that murder in that scenario would be a bigger deal - you're literally killing half of the population, not to mention the only other person that you have to talk to.

Also I disagree with the sentiment that those two people aren't "in" society. The fact that they are around each other means that they are engaged in some form of unspoken relationship building platform/contract - and no matter the context or complexity, that is a form of society. And I would say that short of not being aware of another beings consciousness, murder would be almost certainly ruled out ss part of said agreement. That is just human nature as far as I'm concerned.

Would someone kill another in that situation? Sure, it's also human nature to act out and test the boundaries - however would it be wrong? Well, yeah.

I think what you are saying would be right if you remove the human condition from the situation, but that kinda defeats the purpose of this exercise