That's a very America centric position to take.
It's a very realistic position to take. The fact that it aligns with an American view of things is of no more import than it is to observe that America complaining about electoral interference is the kettle calling the pot black - a view that aligns with (for example), Iran.
Neither the Chinese, nor the North Koreans represent a serious military threat to America. But South Korea, a population of 51 million people, would be seriously fucked up by any conflict that was started. Should we view these humans as disposable and inferior?
Yes, Seoul is in range of the North's artillery. But the North have no real first strike capability.
And their artillery is silence-able via naval and air resources. The North Koreans wouldn't be able to get across the DMZ before being wiped out.
Will some South Koreans die? Sure. But it'll be a short war.
In fact I suspect that the only reason North Korea still exists is because US/China relations are reasonably good. If The Donald makes the Chinese an offer they can't refuse - ie unification of Korea and all US troops out, would the Chinese refuse? Better to have a predictable US ally on the border than an unpredictable fatso with a messiah complex?