When I wrote fights by the sword instead of lives by the sword, I was going by memory of two Bible verses and was in a hurry to get my message posted before leaving home to go to work. However, I wasn't incorrect (see below where Bible quotes says "take up" and "kills with"), since the word I used convey essentially the same meaning as the word(s) used in Bible verses. Your use of "lives" is in harmony with a Greek drama (see below).
But if someone makes a living by being employed in the military to
intentionally kill people, whether by the sword, guns, cannons, bombs,
etc., then I think those verses applies them also, not just villains
killing for fun, money, or power. I realize that others don't think it applies to those in military service (but what if they were Nazis doing the evil bidding of Hitler?)
There are two verses, one which says "take up the sword" (Matthew 26:52 NASB Updated; NWT 1984 says "take the sword') and one which says "kills with the sword" (Revelation 13:10; NASB Updated; NWT 1984 says "kills with the sword") and I have long thought those to verses convey the same message. The Life Application Study Bible - NASB Updated edition at Matthew 26:52 gives the cross reference to Revelation 13:10. The verse in Matthew 26 is the verse immediately after the verse in which someone with Jesus (which a different gospel account identifies with Peter) used a sword to cut off an ear.
See https://en.wikipedia.org/wiki/Live_by_the_sword,_die_by_the_sword . It says in part the following.
' "Live by the sword, die by the sword" is a proverb in the form of a parallel phrase, derived from the Gospel of Matthew (Matthew 26, 26:52): "Then said Jesus unto him, Put up again thy sword into his place: for all they that take the sword shall perish with the sword."
... The phrase comes from the Gospel of Matthew (Matthew 26, 26:52), in which one of Jesus's disciples is described as having struck the servant of the High Priest of Israel and cut off his ear.[1] Jesus is described as having rebuked him, saying:[2]
... The sayings is sometimes interpreted to mean "those who live by violence will die by violence",[5] which some have interpreted as a call for Christian pacifism[6] or even complete nonviolence,
including in self-defense. The passage may also mean that those who use
the sword in a criminal, violent, unlawful way will be subject to
execution by the sword. This would connect the passage to the statement
by St. Paul in Romans 13:4, which uses the same Greek word for sword,
"If you do wrong, be afraid, for rulers do not bear the sword for
nothing." This is also in keeping with Genesis 9:6 where God commanded
Noah, "Whoever sheds the blood of man, by man shall his blood be shed,
for God made man in his own image."
... A very similar line can be found in the Agamemnon, the first book of the Oresteia trilogy of tragic dramas by the ancient Greek tragedian and playwright Aeschylus.[7][8][9]
...
The line differs across translators and is variously understood as "live by the sword, die by the sword" or "an eye for an eye", emphasizing the irony or appropriateness of the means by which he was killed.'
For context about Matthew 26:51-52 see also Luke 22:36, 38, and 49-51. Verses 49-51 show how Jesus applied his words recorded in Luke 22:36, 38. Such was I was stated in my prior post.