I've never denied that I'm pragmatic. Sometimes, killing is necessary.

This does not detract from the fact that it is still immoral by Christian definition. Just that Christian definitions of morality don't mean much to me personally.

The Christian view of the immorality of killing is established by "Thou shalt not kill".

I don't believe that commandment came with any caveats or allowable exceptions to the commandment. I don't claim to be a Christian, therefore I'm not hypocritical about this.

Actually, if I recall correctly, the Hebrew word which the old King James Version translated into "kill" was actually "murder" (and most other translations reflect this). Ancient Hebrew had a distinction between the terms much as English does: "murder" was intentional unlawful killing; the implication being that there is such a thing as lawful killing, which is not forbidden.

I would, in fact, hazard to say that the Jewish Scriptures (at least those included in the Old Testament section of a Bible), don't really strongly condemn war or killing in general: there are certainly plenty of times when it is shown as being righteous and just.
I know less about Islam, but given the history of Muhammad, I find it difficult to see any all-encompassing prohibition on killing any other human at any time coming from that religion either.
The Christian New Testament (if taken separate from the Old) does, admittedly, include some pretty direct statements that seem like they should make all killing antithetical to Christian doctrine. It's hard to fit the idea of a "just war" into the commands about 'turning the other cheek,' 'loving thy enemy,' and the notion that even just hating someone is morally tantamount to murder (the intentional, unlawful kind). In my experience, arguments about Christians supporting war or capital punishment generally have to either rely on Old Testament passages or appeal to the fact that Jesus and the Apostles spoke with soldiers and didn't go out of their way to condemn them.

Anyway, I question whether "Thou shalt not kill" (with "kill" being distinct from "murder") is actually spelled out in any of the three monotheistic religions.

And, as you say, from a more materialistic point of view, it isn't terribly practical.

Yes, I'm well aware that many Christians have a whole host of methods and techniques to dodge the "thou shalt not kill" commandment.

I just find most of them to be rather selective (and thus, hypocritical).

And it isn't an absolute. The Catholics for example tend to be politically opposed to both capital punishment and war (which is consistent).