That "truth" obviously depends on which side it is that is recruiting one:

if cells in your body who are being run by viruses "take up arms", they are taking up arms against your life, for virus's dominion.

if ideological-supremacism gets people to take up arms for their cause, they are arming to war against real peace.

if cells in your body who fight infection get other cells to "take up arms", they are fighting together against pathogen's dominion.

if people take up arms against ideological rabies's highjacking of our world, or of its dismantling/exterminating civil-rights, then they are fighting for the existence of civil-rights & actual/possible peace.

Ukraina's fighting for its life is right, Russia's fighting to genocide Ukrainians isn't.

.: whether one's taking up arms is morally right or not, has exactly to do with one's opposition-to, or accommodation-of, or even helping-of, the kremlin's genociding-mission.

Same goes for Hamas's deliberately sacrificing the Palestinian people for sake of getting Israel's nihilistic sadistic psychopathy to show enough that the entire surrounding region will ( within a decade or so ) prefer "martyrdom" while annihilating Israel, than to tolerate Israel, genocider who claims "God", to continue to exist.

Hamas & Israel both demonstrate DarkHexad: Narcissism / Machiavellianism / Sociopathy-Psychopathy / Nihilism / Sadism / Systemic-Dishonesty..

https://www.haaretz.com/israel-news/security-aviation/2024-02-04/ty-article/.premium/israeli-army-its-admits-staff-was-behind-graphic-gaza-telegram-channel/0000018d-70b4-dd6e-a98d-f4b6a9c00000

Israel's full allegiance to DarkHexad is visible in what IDF was carving in God's eye, with that operation.

Israel's longstanding declaration that it will nuke ALL its neighbours if any ONE overruns it, a nuclear-mass-shooting, is itself proof of its DarkHexad nationalism, which claims that God authorizes it ( the Ezekiel 39 "justification" for genociding Palestinians now, the rest later, e.g. )

Nobody should bother pretending that our countries haven't done exactly the same commitment-of-evil that these 2 examples are doing:

the deliberately-infecting entire shiploads of fabric, with smallpox, before sending them to the Americas, to holocaust the Indigenous peoples, our "Residential School" genociding of their lives ..

https://duckduckgo.com/?q=hopi+alcatraz&t=fpas&iax=images&ia=images

is pictures of men whose "crime" in our law was that they wouldn't agree, in writing, with their children being taken, at gunpoint, by us, & put in residential schools .. so we rounded 'em up at gunpoint, & shipped the survivors of our enforcement off to Alcatraz..

That was every bit as evil as what the kremlin-war-on-Ukraina or Israel's genociding now do.

History is unspeakably ugly.

The Catholic inquisition's torture-murdering war against primarily women, & secondarily Jews, "in our Lord, King of all Jews"'s name, had nothing whatsoever to do with the religion of the woke socialist convict/felon that Yehoshua "Jesus" benJoseph was, in their bible.

Africa, whose 2 million year history of tool-using hominids, nearly-all of its history is unrecorded, but the European slave-industry was fed by Arabs & Africans, in Africa, who were leveraging their local authority, turning those who weren't "with" them into "profit"..

the evil committed by the Aztecs, some tiny fraction of it recorded, when records began being created..

the "conquistadors" & their evil against Indiginous peoples..

It's inseparable from our race's history

It isn't that "taking up arms" is wrong, it is that either:

• taking up arms for ideological-supremacism, XOR
• refusing to take up arms against ideological supremacism

both help ideological supremacism.

Helping ideological supremacism is an active crime against civil-rights being able to exist.

it is a crime against right Principles.

As Martin Luther King Jr pointed-out, silence, itself is the crime of accommodating evil, when evil is acting.

( the "bystander effect" of accommodating a crime against someone, which depends on the culture & the individual-development vs collectivity of the bystanders, is also in the domain of this question, obviously ).