Literal

Cursed are those who refuse to do the LORD's work, A curse on anyone who keeps their sword from bloodshed! (Jeremiah 48:10)

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Just for the record, this is not a metaphorical statement it's literal. Yes when the verse say's "A curse on anyone who keeps their sword from bloodshed!" means just that. We have good evidence from Jewish source that this statement was taken literally. Take for example

Joab the son of Zeruiah, was the nephew of King David and the commander of his army, according to the Hebrew Bible. What did Joab say about this statement?

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Joab took a sword to kill him. The teacher said to him: Why do you want to kill me? Joab said to him: As it is written: “Cursed is he who does the work of the Lord with a slack hand”(Jeremiah 48:10), and you taught me incorrectly. The teacher said to him: Leave that man to remain as cursed. This is a sufficient punishment; there is no need to kill me. Joab said to him: It is also written: “And cursed is he who keeps back his sword from blood”(Jeremiah 48:10).  (Talmud Bava Batra 21b:2)

Notice how Joab the nephew of king David killed the teacher because he did not teach joab correctly by following the lord. Joab was quoting Jeremiah 48:10 to prove this was a literal commandment from yahweh. Ask yourself are Christians doing the work of the Lord by following the Torah ? They  say every word in the Bible is from God, yet reject the teachings of the Old Testament.

next time they say, the Bible does not promote violence ask them why then did yahweh curse those who slack doing his work and refrain from using their sword? Heres more teaching from the Mishna

 It is explicitly stated in the Tradition that, “Cursed be he who does the work of G-d sluggishly, and cursed be he who keeps back his sword from blood” (Jeremiah 48:10). However, anyone who does fight with all his heart without fear, and his intentions are only to Sanctify the Name, is promised that he will not be harmed and nothing bad will happen to him. He will build an upright home in Israel, and he and his children will earn merit forever, and merit The World To Come, as it says, “certainly, G-d shall make for my master a faithful house, for the wars of G-d does my master fight and no evil will be found with you all your days…And the soul of my master will be bound with the living, with the Lord your G-d…” (I Samuel 25:28-29). (Mishneh Torah, Kings and Wars 7:15)

the teaching from Jeremiah is clear, you are cursed unless your sword is drenched in blood.