And we also have to abandon 1.3 billion people in the process. For example, people in North Korea are starving. It's just we don't pay much attention to it. Is this evil necessary?
Can we save them all? We've given North Korea free grain shipments before to help their population, the government just resold it for cash. And we can't topple a government that's willing to use nuclear weapons just to stay in power.
At some point you just have to wait for a better chance. The Soviet bloc was just as unjust and abusive, but before Gorbachev, there was simply no chance of getting rid of it without a hundred million dead in the process. We can only hope that North Korea (or China, hypothetically) appoint benign reformers at some point.