Government has consequences. That's why democracy is so important. This is especially true with regards to foreign policy. If a country threatens another such that the threatened country's only viable defense is to attack the civilians of the aggressor, that would be a totally legitimate tactic of war.

Taking out North Korea's nuclear capability while preventing a counter attack on South Korea will probably involve the deaths of many innocent North Koreans, since North Korean artillery is spread widely throughout the southern part of the country. That is tragic, and no small part of why we've allowed this madness to go on for so long. But at some point a people must protect their security, and do what must be done.