If we had treated Vietnam the way we treated Cuba (i.e., acted like we were going to overthrow Ho Chi Minh and then quit right after we started), there would have been far fewer casualties.
But there would be other consequences.
Vietnam would still be a Communist backwater like Cuba, instead of a burgeoning proto-capitalist nation that is begging for Americans to come teach business and teach Christ.
The communists wouldn’t have stopped with Indochina, because they never stop. Their military money would have been free to attack Taiwan, or reinstigate the Korean War, or invade Japan from the Kirils—or even attempt to take over Alaska, especially if we didn’t try stopping them in Taiwan or Korea or Japan.
LBJ fought the Vietnam War as stupidly as Hitler fought Operation Barbarosa, and for the same reason: he wanted to run the strategy and the tactics, and sometimes even the operations. Nixon just wanted to end the war without looking like he was ending the war (unlike Biden, who ended Afghanistan without giving a damn how it looked), which extended the war for four more years than necessary. It was the way we fought Vietnam which made it, to use a word no one hears these days, a bloodbath.
Full Disclosure: I lived in Japan 67-70 as a Navy brat and was as close to the war as one could get without being in Vietnam. Later, I was entering AFROTC when the draft was suspended in ‘73, and told by the CO at the college that we wouldn’t be needed, which was how my military career ended before it began.
We were members of a surf club at Camp Pendleton, learning from the jarheads what war was at an early age.
Same thing with signing up on B day number 18. The recruiters told me to go to college, no need. Five years later still no need