And don’t tell me the Americans didn’t do a lot of those things you just named. Wasn’t just “rice”.
Maybe not surprisingly, the war was just as messy on the other side. Lots of internal dissent and power struggles over how it should be run. Giap and Ho Chi Minh (prior to his death) were much more on the "slow and steady" approach, open to negotiation, while Le Duan pushed the "go for broke" approach. Le Duan eventually won that argument.
Giap did not believe the Tet Offensive was the right approach. In the run up to Tet '68, Giap was conveniently in Eastern Europe for "medical care" while his staff was jailed. Ho Chi Minh had already been relegated to a figure head at that point and didn't have much political power (he was also quite ill by then).
This makes it doubly baffling about how the US approached the conflict. Instead of siding with a then amenable Ho Chi Minh, which would have made Vietnam if not an ally of the West, at least not totally hostile, they sided with the colonial power (the French) and against the national liberation movement. They even supported a dictator in the South that was so bad and unlikable, they later had to green light his assassination. And the ones that followed were inept and corrupt.
There was just no way the US, siding with colonialism and conducting a war whose major success metric was body count (i.e. kill them all and pray they are all commies) would have been able to win that war. Short of totally wasting the whole of Vietnam, North and South, in which case they would have lost in the court of world opinion.
Also, if you consider the Chinese response to these wars where the US was restoring the colonial system in a recently liberated Asia after the fall of Japan, it had desirable outcomes. China stifled it's economic growth by moving it's economic/industrial base deep into it's interior[0], since it felt that the cities on the coast were vulnerable to naval attacks, and areas near the borders of korea and vietnam would be vulnerable to US ground attack. This probably set back the Chinese economy severely, for decades.
Edit: And, of course, you could argue that "kill them all" would be a successful dissuasion to prevent other states from declaring independence. eg. Indonesia and Philipines. Though I guess the effect on them was probably mixed(?) You have to consider that Korea is still partitioned, and South Korea is still a vassal state and military outpost of the US. Although the US was unable to achieve that outcome in Vietnam, it was not an unreasonable goal at the outset.
The "domino theory" was definitely in play, but that was about fear of Communist takeover in already-independent countries.
https://en.wikipedia.org/wiki/Suharto
https://en.wikipedia.org/wiki/Ferdinand_Marcos
Another interpretation is that that is a tired old canard which maintains a life-beyond-death as a necessary illusion which assists the beholder in doing their patriotic duty: maintaining a positive view of the foreign policy of their own nation.
Edit: but yes, my original response was sloppily worded. I didn't mean "declare independence", but rather, "actually achieve independence", my bad.