>There were lots of stirings
> about rationalism both in thought, and in institutional practice, and
> the society at large. I mean Vietnam made absolutely no rational sense,
> etc.
==============================
It made sense to US politicians and generals worried that a Communist-led
revolutionary insurrection in Vietnam could inspire others in the region,
and confident that their vastly better-equipped forces could suppress it.
The progressive buildup of US ground troops was based on a series of
miscalculations, but this only became evident as the conflict progressed,
and finally prompted the Americans to withdraw.
Arguably, then, Vietnam wasn't irrational in terms of US imperial interests, and in fact could only be understood with reference to these, which is how radicals like myself viewed the war. On the other hand, there were also many horrified liberals in the antiwar movement who regarded Vietnam as a somehow "irrational" betrayal of the traditional American ideals they had been weaned on, notably support for democracy and the principle of self-determination.
Perhaps, as you suggest, there are hints here of the wider issues raised in this thread.