Vietnam was a lot more complicated than just a bad decision to be involved or a waste that should have never been.
Yes, the "hawks" (in uniform and in civilian leadership) took advantage of the Gulf of Tonkin incident to escalate from assistance to direct action, and yes we failed to appreciate/took too long to realize just how bad the Diem government was (what we'd nowadays sanction for human rights abuses- although it wasn't as bad as Uncle Ho). We also didn't appreciate that was a civil war as much as it was a war of unification with outside intervention. The domino theory seems trite nowadays but the effort we poured into the Vietnam War did deter communist aggression (didn't eliminate by any stretch but it did impact adversary nations' foreign policies).
"What if" we hadn't gotten involved or what if we'd got out in the mid-late sixties, instead of sticking around through Westmoreland's doctrine changing to Abrams'... it's kind of a scary thought. I think ceding South Vietnam c1965 would have empowered the eastern bloc, a lot.
It's a debate that will never really conclude, I mean thesis-level stuff that a lot of people have dedicated years of their lives to figuring out.