Job of a soldier is dangerous, and many who take the sword will die from the other side's sword. However I wouldn't go so far as to declare all soldiers sinners. Voluntarily dying to save others is not a sin; far from that. I won't offend you by citing a verse to prove that :-)
A good Christian, if he was wounded by Adam Lanza but found himself in position to shoot the killer, would do so;
Please give me Bible verses to make the case for this. Make sure you don’t contradict the ones I already gave.
I have done so already, in the link of my earlier comment:
Luke 17:2
It were better for him that a millstone were hanged about his neck, and he cast into the sea, than that he should offend one of these little ones.
This is a pretty violent threat. Note the grammar, it is very consistent across translations. Note the passive voice forms. Someone else "hangs a millstone around his neck" and then "casts him into the sea." Who, in your opinion, is supposed to do that? Is that an empty threat? Was it said for no reason? If it is "better" for the offender, is anyone supposed to do this "better" thing to him? The instructions are quite specific.
Or I can even offer a simpler test. Imagine that a violent killer walks around a playground and kills children one by one. One Christian, with a loaded 1911 in the holster, is present and can act. He orders the criminal to stop. The criminal ignores him. (Why not, the killer is not a Christian just by the nature of his acts.) What would a true Christian, per your definition, do? A child dies every ten seconds; you have no time for prolonged meditation. Your action? Note: by law you are not required to intervene; you only need to do your best to report the crime.
There is one important factor here that you do not make use of. This factor is notably missing from the quotes that you mention - and it is very prominent in my quote. That factor is the person who is wronged. If someone harms you personally, it's your personal affair. You can do whatever you want, and if you are inclined to forgive you are free to do so because it's only your own health, life and property that are at stake. You have authority to deal with these items. You can even allow your throat to be cut, though it borders on suicide.
However in many cases you are proposing to forgive a criminal for harm that he caused to someone else. You do not have authority to do so. Your authority stops at your own body, and at your own chattel. You cannot forgive a killer for killing a stranger. It is simply not your right to do so.
Now that we established that, you are faced with a situation where you can help others (with their life, not with some trifles!) - and you do not. You choose to let them die, even though you can have the march of death stopped at any time. You have pure evil in front of you - and instead of stepping up to the plate and doing your part you ... you ask someone else (God) to do it for you! Is He supposed to descend from Heaven upon your command and smite the killer? Or, perhaps, He has already given us detailed instructions on how to deal with this problem on our own?
YOU SAID: However I wouldn’t go so far as to declare all soldiers sinners.
I would not either per Romans 13:4 and Luke 3:14.
YOU SAID: Imagine that a violent killer walks around a playground and kills children one by one. One Christian, with a loaded 1911 in the holster, is present and can act. He orders the criminal to stop. The criminal ignores him. (Why not, the killer is not a Christian just by the nature of his acts.) What would a true Christian, per your definition, do?
A true Christian would be ...
1) running a deliverance ministry, so “psychos” are delivered of murderous demons per http://holyrestoration.weebly.com/deliverance.html
2) praying and fasting and binding the powers of darkness across the nation so such things would not happen
YOU SAID: However in many cases you are proposing to forgive a criminal for harm that he caused to someone else. You do not have authority to do so.
Wait, say my daughter is killed by a murderer. Should I not grieve? Would this not be a challenge for me to obey Jesus’ calls to forgive?
For if ye forgive men their trespasses, your heavenly Father will also forgive you: But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
Matthew 6:14-15
And when ye stand praying, forgive, if ye have ought against any: that your Father also which is in heaven may forgive you your trespasses. But if ye do not forgive, neither will your Father which is in heaven forgive your trespasses.
Mark 11:25-26
Indeed, I cannot forgive man’s sins so far as their standing with the LORD is concerned. The murderer goes to heaven or hell based on how they respond to Jesus Christ. What IS my responsibility is that I do not hate that offender in my heart, and that I don’t be bitter against them. Hating or holding unforgiveness jeopardizes MY soul.
YOU SAID: You have pure evil in front of you - and instead of stepping up to the plate and doing your part you ... you ask someone else (God) to do it for you!
I am stepping up to the plate by working to spread the Gospel of Jesus Christ, and using my God given authority to come against evil in this country, and to pray for sinners to get saved, and for Christians to stop backsliding.