North Korea is a horrendous hole of a country, but that does not justify robbing U.S. taxpayers to finance an invasion and occupation that will likely, if past wars of "liberation" are any guide, involve the pillage, rape, and murder of innocent civilians. Also, given the imperial overstretch of the U.S., any new war would almost certainly involve conscription, which is, of course, legalized slavery in that it completely deprives the conscripted of their natural right life and liberty.
No war of aggression is ever justified. Only defensive wars are just, and those are not even really "wars," in my opinion. Defending yourself against aggression is not waging war.
Communism cannot last. As Ludwig von Mises brilliantly explained in "Economic Calculation in the Socialist Commonwealth," communism is doomed to implode. The lack of market-determined prices prevents a rational allocation of resources, leading to massive surpluses and shortages. Furthermore, the lack of property rights destroys the marginal utility of labor (demotivating people from working hard or even at all) and creates a tragedy of the commons (depleting all property of its value without regard to the future). There is no need to fight communism, as it sows the seeds of its own destruction. Communism will collapse, and something better will rise from the ashes.
Also, how exactly are North-Korean "concentration camps" any different from the booming prison industry of the U.S.? The U.S. incarcerates more people per capita than any other country in the world, including the Stalinist USSR, and mostly for victimless crimes. The U.S. has no moral authority whatsoever.
"Yesterday we obeyed kings and bent our necks before emperors, but today we kneel only to truth." - Kahlil Gibran