Yeah, everyone is an expert 60 years later. No context, no consideration of treaties we had. No consideration of anything except "it was 100% wrong". This is what has happened to our culture, everything is 100% right or wrong. The only difference between Korea and Vietnam is we lost in Vietnam. In Korea we committed to winning, much to the detriment of several million Koreans (mostly North Koreans). In Vietnam we did not commit to winning.
I have a friend who sat in all the meetings with Norman Schwartzkoff in Saudi when they were planning the invasion of Iraq. He said that in almost every meeting there was one mantra that was repeated over and over regarding the Vietnam War. That mantra was "Never again" Meaning we will never again go to war without planning to win it. People were astonished when we went through the Iraqi army like sh[t through a goose. That is what you do when you plan to win. We never did that in Vietnam,, That is why we lost.
Now whether you believe it was 100% wrong or not to prosecute that war, out politicians decided not to. When we were in the Korean War they decided to see it through, so we won, or at least we decided to stop fighting. War is a terrible thing, it is the ultimate tool of diplomacy.