Is that belief justified by authoritative texts by Krishna is something Baha'is would ask. Your interpretation of the Bhagavad Gita may be different from mine. Is what is recorded in the Bhagavad Gita in all cases what Krishna said?
Everyone has an agenda or POV. To get what the conversation was between Krishna and Arjuna, one needs to read the original Sanskrit and understand the context or read several versions and the commentaries and weed through them.
Sanskrit is notorious for having the most synonyms in any language. Krishna can mean dark, black, attractive. Krishna paksha is the dark fortnight of the moon cycle, for example. Pretty diverse meanings for one word. Sanskrit is also a nightmarishly inflected language.
When J. Robert Oppenheimer translated Bhagavad Gita 11.32 he translated it as “Now I am become Death, the destroyer of worlds”. But that’s not at all what the verse says:
śrī-bhagavān uvācha
kālo ’smi loka-kṣhaya-kṛit pravṛiddho
lokān samāhartum iha pravṛittaḥ
ṛite ’pi tvāṁ na bhaviṣhyanti sarve
ye ’vasthitāḥ pratyanīkeṣhu yodhāḥ
The Supreme Lord said: Time I am (literal translation, kalah + asmi-> kalo’smi by rules of Sanskrit grammar)
the source of destruction that comes forth to annihilate the worlds. Even without your participation, the warriors arrayed in the opposing army shall cease to exist.
sri bhagavan uvaca—the Personality of Godhead said; kalah—time; asmi—I am; loka—the worlds; ksaya-krt—destroyer; pravrddhah—to engage; lokan—all people; samahartum—to destroy; iha—in this world; pravrttah—to engage; rte api—without even; tvam—you; na—never; bhavisyanti—will be; sarve—all; ye—who; avasthitah—situated; pratyanikesu—on the opposite side; yodhah—the soldiers.
This is Prabhupada’s translation. Śrī Bhagavān is not “The Personality of Godhead”. Prabupada usually uses Supreme personality of Godhead”. It doesn’t mean that at all. It simply means “the Blessed Lord”.
So my point, getting back to Oppenheimer, his translation was either simple error, which I actually doubt, or a deliberate mistranslation to underscore the horror of what he saw, for dramatic effect. Śrī Krishna is telling Arjuna not to mourn for those who, because of Time, are already dead. Arjuna was Kshatriya, he was duty-bound by birth to fight. He didn’t want to because he was going to kill his cousins, his beloved grand uncle (Bhishma), his teacher. In the verses surrounding this one, and preceding chapters Krishna explains the nature of the soul and existence. He’s not talking about horrible gruesome destruction at all, or even the horrors of war.
Therefore, one has to know the context and the language to get a true understanding. I like Prabhupada’s English translations because they are rather poetic but his commentaries are often completely unlike the Sanskrit, and even unlike other translators who are closer in commentary to the Sanskrit.