The only thing wrong with this movie was that John Wayne's character, COL Kirby, was not Ranger qualified.
Forget the trite lines and poor special effects. Viewers who criticize this film for not having a meaning or realism miss its point. This was John Wayne giving support to the troops the best way he knew how- by making a patriotic John Wayne movie. Nobody ever criticized Bob Hope for entertaining the troops, so why pan the Duke for doing the same? This movie was no more borish or weak than the Saturday morning serials we used to cheer in the 30s, 40s and 50s. If you want a deeper message see The Searchers (and if you look closely, you WILL see some parallels...)
North Vietnam and the VC had great PR throughout the war---they managed to dupe most of the world into believing they were peace loving victims of Western imperialism. For some reason, the press never focussed on their use of cold terror and outright mass murder to force their aims on the people of RVN. People forget that we were not in Vietnam to save Vietnam; we were there to stem the tide of world wide communist expansion. We didn't lose in 1975; we won in 1989 when the Wall came down.
So John Wayne's "The Green Berets" was a little schmaltzy. Warm beer tastes flat, but better than no beer. The actors' roles, on both sides, were caricatures of their respective types.
I saw this movie when I was stationed on Okinawa in 1969. Everyone cheered, no one whined. No civilian I ever met liked it. So what? Regardless of politics, most Americans who served in Southeast Asia did so honorably. This is an honorable movie.