That is the point. We want to destroy their civilian population, transportation, infrastructure and industrial capacity. In WW2 we firebombed 65 Japanese cities and killed hundreds of thousands. It decimated their will and ability to wage war.
Using nukes would have turned our allies even further from us - and we had very few standing with us to begin with in Vietnam.
We used nuclear weapons on Japan in WW2 which killed 220,000 people. But none of our allies turned against us because of that.
I’m sorry, big guy - but we weren’t targeting civilians in Vietnam nor were we in a desperate total war for our own survival as we were against the Japanese. Entirely different situation. We also had the Soviets and the Chinese openly supporting the NVA - and there in large numbers. How much would it have taken for a nuclear response if we killed a bunch of Sovs in a tactical nuclear attack? I served in Vietnam for 18 months in combat and I am very proud of the men I served with and they way we conducted ourselves. We protected the civilians, we didn’t victimize them.