On piety, lies and murder

"מדבר שקר תרחק ונקי וצדיק אל תהרג כי לא אצדיק רשע."
(Keep yourself far from a matter of lie; and the innocent and righteous slay thou not; for I will not justify the wicked)

This posuk seems to jump from one extremity to another; distancing oneself from gratuitous lies and falsities is a pious property that's far from being a common one; yet, every code of every society known to man, at least in theory, would try and prevent systemic killing of the righteous and innocent. And what's the connection to "I will not justify the wicked" ?

Modern forerunners of the true atheist ideology (Hitchens being probably the most visible representative) theorize in what they consider one of their strongest arguments that religion in general has done more harm then good, and whatever good the religion did deliver - could've been achieved at least as good and probably in better fashion by an irreligious man adhering to a moral codex. They argue that common values such as respect for human life and property ownership aren't divinely given rights but are natural rules by which humanity would have, and will, abide even in absolute absence of religious thinking and even in presence of proactive atheism (a la Soviet Union circa 1930's). The more viral and repulsive strains of atheism known as "Atheistic Judaism" a/k/a "Humanistic Judaism" philosophize on the merits of atheistic ethics and how much better the world would be without religion, yet with a set of moral standards (usually, they theorize using moral standards that appear substantially higher then those proposed by religious norms).

Without delving too deep, what they're basically saying that people (themselves) will not kill, steal, rob or rape. The less obvious moralities - adultery or lying - are, I guess, middle ground, and usually aren't discussed. What they would like everyone else to forget, or not to know, is a well accepted and not at all controversial result in game theory with consequences in psychology and sociology; that in the "long run", participants will resort to behavior that "rationally" benefits them both - or will get booted out of the game. What's meant by "rationally" is the implicit valuation of risks, rewards, costs and payoff - current and future - associated with a decision, a choice or an action. Even the mildly theistic Pascal's wager, which is unfortunately the basis for too many people's inner beliefs, is based on this principle. So ultimately, someone who believes in possibility of future reward and punishment of unknown magnitude will often use that to offset whatever immediate benefit one may realize from "immoral" behavior. Meanwhile, the atheist who does not believe in reward and punishment beyond legal has no reason not to commit the crime other then an irrational reason of having to live with his conscience; and Darwinism is the first and foremost discipline that mandates that humans that were to abide by these irrational rule of conscience would be booted off the ladder quicker then you can say "natural selection".