The North had Hanoi Hilton and Desert Inn and plenty of places it kept and tortured political dissidents and American POWs in violation of the Geneva convention. The Vietnam War was a giant mistake, a huge blunder, however, as others have mentioned the Korean war was fought under similar pretexts and no one regrets the U.S. stepping in to save South Korea.
I don't know whether or not the U.S. made all the right choices in the Cold War against the U.S.S.R. Would you prefer a world in which the U.S. hadn't engaged at all against Russia or stayed completely out of Asia (as well as European conflicts)? I don't know if the world that exists today would be better or worse off, really hard to say.
* The existence of films critical of the war does not imply that the mainstream "serious" political opinion of the day (that you would read in national newspapers, for example) went beyond calling the war a "quagmire" or "disaster", then with a justifying "but...", usually mentioning Domino theory or Containment as you implicitly do. I disagree with that assessment.
* The fact that North Vietnam (or Japan, or anyone) were awful in their treatment of PoWs doesn't excuse the US treating civilians in South Korea terribly. You are responsible for the foreseeable consequences of your own actions (or a close ally's actions), not someone else's. It's not "whataboutism" to focus on the effects you can actually control, even if it's historical. You can't change the past, but you can learn from your own history and understand what is "foreign propaganda" and what's actually just an uncomfortable truth.
* I can think of a few US interventions in the Cold War that seem to have hurt more than they helped, even with info available to decision-makers before committing to them. Vietnam is one of them.
Edit: I don't want to contribute to a pointless back-and-forth asking leading questions of each other, and don't have the time to go into major detail or link reading material, but I just thought I'd at least elaborate my thoughts more on the "blunder" comment, and the point about focusing on your own actions.