Some mild comments - since I pretty much agree with your rant - so, take these in the spirit of "refinements". All quotes are from you.

Viet Nam the war was effectively decided and over when Johnson announced he would not run for reelection.
Decided, yes (Johnson blinked hard); but, unfortunately, not over (you know the KIA and WIA totals better than I - and the 1968-1972 iterations of the war did much of the damage that plagued the military thereafter).

By the time of the 1968 election the Democratic Party and its supporters were as opposed -- or perhaps more -- to the war as the Republican side had been.
More complex than that. I had feet in both parties at that time; but discussion of the complexities would not be useful to this thread. After the election, most Republicans and some Democrats lined up with Vietnamization; while most Democrats and some Republicans opted for something akin to Get Out Now - so, the rather clearly defined lines in the 1972 election.

The major difference between Viet Nam and all our other wars ... Baby Boomers .. anti-draft, actually... They wanted to "change the system." They did, they became the system ... so in this war, we get "I support the troops but not the War" from a bunch of flakes that would go berserk if their son or daughter decided to be one of those troops.
Good rant - get it out of your system.

There's a Bill Corson story, perhaps apocryphal, where he spoke before a large college audience. He asked all the guys to hold up their draft cards. The audience thought - "Oh goody, we'll have a draft card burning." Not quite, Corson said something along these lines: "Now, most all of your cards have 2-S (student deferment) on them. What I want you all to do is contact your local draft boards and have them changed to 1-A. Then, I want you all to request immediate induction. If you then feel as strongly against this war as all your speakers here have said, you should then refuse induction. You then will be prosecuted and probably serve time in prison. If you really believe what you say, that is how you will do your part to end this war." He got no takers and some booing.