I was taught in high school that pure communism is the best form of government. The trouble is that human nature will not allow pure communism to exist. Imperfect humans can be petty, arrogant, jealous.

I personally would not see a communist country with no dictator, no troubles and power in the hands of the people as a threat, so I personally would not see any need to force change in it.
I would, however, keep an eye on the country. I would want to make sure a dictator does not emerge. I would want to make sure the country does not attempt to ally with my enemies.
But then, these are things I would want to do with any country, not exclusively one that happens to have a communist government.