I was very young when the war ended, and while I think it was a worthy cause I don’t see any permanent solution open to us at the time. South Vietnam had to defend itself, and simply wasn’t able to do so; Tet was won by US troops, and US airpower beat back the Easter Offensive in ‘72. There was no way the US, which couldn’t successfully control South Vietnam, was ever going to occupy the North (and endure the losses that would entail). While there have been countless comparisons to Korea, the South Koreans were much more determined to keep their freedom from the North - and many people fled south when the chance presented itself (both before and during the war) because of the brutality of the North’s government.