The cause was just. The government of SV may not have been good, but it was good enoough to allow the orphans to be cared for, and to allow Americans to help.
For the sort of effort that got put into Nam, that in my view is not good enough. It's certainly not good enough to draft anybody into.
In Nixon's place in Feb of 69, I'd have called the joint chiefs into a room and laid out some sort of a law, like what if anything do you guys figure you can accomplish in Nam in a year starting from now, without using draftees in combat roles, without using vast sums of money, and basically just using the kinds of assets you use to play such games with, professional soldiers, soldiers of fortune, air power, our battleships, and special ops. I'd have had no qualms about any sort of an assault on North Vietnam under those rules. If they'd told me they couldn't accomplish anything in Nam in a year with those constraints, I'd have ended the whole thing immediately.