I don't think Dark Knight is related to any calamities, and they're considered to be heretical in Ishgard (at least by the openly-bigoted Temple Knights). Most of the other city-states seem to be blissfully unaware of what a Dark Knight even is, though I can't imagine they'd take too kindly to a job whose skills, much like Necromancer, involve desecration (Salted Earth), vampirism (Abyssal Drain and Souleater), turning oneself into the undead (Living Dead), and general practice of Dark-type magics normally wielded by Ascians.
But another point worth discussing is that Dark Knight has a specific and necessary role within Ishgardian society, much as Rogues do in Limsa and White Mages in Gridania. Part of the BLM storyline is trying to plead legitimacy for the study to a skeptical Thaumaturge's Guild in Ul'dah, not too far removed from other jobs like AST or BLU trying to do the same.
In the Physical DPS storyline in Shadowbringers, a character cracks a joke that implies Necromancers were a somewhat common practice in the First at one point; obviously we're missing the context of the severity, but there's enough ambiguity there for leeway.
So on the one hand, you could have the argument that you're trying to resurrect a dead art (no pun intended) that was lost after, say, the fall of Belah'dia or the elevation of Gelmorran society. Much like Summoner, most people will raise an eyebrow but kinda ignore it after a little explanation that it's not what they think and that you have the special approval of <insert Grand Company leader here> to test it.
And on the other hand, you have the plausibility that it's actually a legitimate practice in some areas, like the First or possibly even Ul'dah (since they still secretly keep the zombification powder once used at Sil'dih) -- perhaps by a group that works on laying Ashkin back to rest, for instance, or hunting criminals much like Dark Knights -- so long as you have the proper authorization and stick to strict rules, as with White Mages.