North Korea's instability and incompetence are the exact reasons why intervention is necessary. Those with nothing to lose can risk it all without risking anything, which makes them incredibly dangerous to the stability of the world. At the same time though, we can't intervene to the point where they feel pushed against a wall for the same reason. We just need to try to softly guide them to stability.
North Korea has been making constant threats against the world and building up their military. We cannot just overlook these threats. North Korea must understand that there are consequences for these threats and the world will not just take them sitting down. They may not actually do anything with their military, but the fact they're threatening us is just provoking us to step in.
Yes, we should limit North Korea's military capabilities. This should be handled by the U.N. Security Council and sanctions should be put in place against North Korea if they fail to comply with reductions and U.N. inspections to ensure that there are in compliance. Kim Jong Un is not to be trusted. This is a man who just had his own uncle executed.
Yes, other countries, beginning with China, have the responsibility to limit the damage that North Korea can do in the region and across the globe. The nation's leadership is clearly irrational and dangerous, and China has long protected its Communist cousin from the consequences of its actions. Missile tests and seemingly random executions mean that North Korea is careening toward chaos.
I think North Korea vastly overstates their military capabilities in general, I think the only threat North Korea poses to the world is to attack South Korea, North Korea would never attack South Korea because they know the entire world would unite against them and would attack them within minutes of doing so, so overall I don't believe other nations should act against North Korea.