What's so bad about morality being a mere human's construct - in other words, the notion that there is no "stone tablet" of morals? In fact, I think the notion that morality exists objectively, like some looming Platonic figure, raises more questions than would be solved by such a condition.
I think the best way to construct this "morality" is just to say that it's got a quasi-mathematical existence, it's axiomic, and it's all augmented by empirical/logical reasoning.
Why accept it, why be moral? I feel the same way about this question as I do about the question of why somebody who believes "if A, then B," and also believes that A, should also believe that B.
"Torture is a relative morality, as such, when a subculture like an intelligence agency tortures a terrorist, then it is allowed and it is moral. Any moral 'critique' of the torture is tantamount to a universal moralist rule: Torture is universally bad."
Torture is universally bad, with the exception of imperatives which are heirarchally superior.
"On the other hand, if morality is defined as "the way people make decisions", then of course everybody is moral and morality exists."
It's more like "the way people ought to make ...
One theory (The Matrix spawned a lot of philosophy talk, and even books) was that, unbeknownst to the machines themselves, they couldn't simply kill off the humans - for ethical reasons. I mean, there are obviously more efficient ways to generate energy, but the robots couldn't kill off their creators - so they came up with this elaborate scheme of harvesting energy from their bodies, and never thinking much about how they were actually losing energy in the process.