If the issue of killing and morality is expanded to include all of huuman history, much of the nit-picking debates above are easier to resolve.

   Throughout the ages humans have "killed for gain". Our cave dwelling ancestors did.... Alexander the Great did... Ghengis Khan & the Mongols did... the Romans did. The list is endless.

But, as civilizations grew, it became obvious (to some) that indiscriminate slaughter for personal or political or cultural gain had problems. Some 'resolved' the issue by adopting moral creeds based on supposed religious themes, some (like Kant) by simply arguing that it was not **rational** to "do unto others" what you wouldn't want "done to YOU".
   Obviously, "killing for gain" still occurs in many forms - both by individuals and by groups who rationalize about their 'privileged status'. What this means is that ... hold on to your hats... **morality is subjective**. It is relative to circumstance and culture and religious belief and other such categories. Yes, certain passages in the Bible were , and 'killing' and 'murder' were sometimes considered identical and sometimes carefully separated.... according to culture, specific religious affiliation, and personal circumstance.
   There is obviously a set of rational reasons for society to define and regulate what, if any, 'killing' is permitted ... and by whom: but no universal agreement as to what the definitions & regulations should contain or who should define and regulate them.
Should capital punishment be permitted at all? Should it be left to legislatures & judges, or be a matter of voting by the citizens? (Cue 27 pages of ranting debates).

It is fairly easy to clarify what ancient texts said about killing & murder, and various of you have done that.... but it is NOT easy to proscribe which interpretation OF those texts should be universally accepted---- simply because we silly humans all are able to rationalize and make decisions based on subjective criteria!

All of us are subject to certain laws about killing & murder, but we all know those laws are often ambiguous ...and even when fairly clear, are not always fairly applied.

This thread was begun to ask about religion, but I just tried to make the point that religion MUST be seen in the larger context of historical analysis to even begin to understand what it all means.