This happens all the time in DF worlds so you'd expect those types to be weeded out quickly, or for the civilization to collapse, whichever comes first. A world that guarantees goblin attacks wouldn't be brimming with individuals that can't deal adequately with the consequences of surviving one.
Most of the dwarves you get as migrants more often than not never seen war. While I agree that the "buff" received by ones who were soldiers in worldgen is awfully meaningless (1st level Discipline at best), for the rest the point still stands.
The horror of seeing dead humanoids is instinctual, especially when it comes to their mutiliated corpses. In real life, it can even cause sudden vomiting or fainting, so yeah, nothing pleasant.
There was an interesting workaround, proposed on reddit, on how to make corpse-horror more balanced without making all dwarves natural-born sociopaths: apply some sort of cap on how much 'seeing a dead body' thoughts a dwarf can get in a token period of time. "Death of a million is a statistic" and all that. It simply makes more sense than a dwarf counting all the corpses on a battlefield and feeling personally affected by each one; and more sense than a dwarf who doesn't really care about
ten corpses, but finds
twenty a bit unnerving already.