But the thing is, certain American's (you know they would take offense at you calling them Yanks...) did actually enjoy killing civilian Vietnamese. You can get these types in the army, and I'm taking a wild guess that you have no idea of the effect a dirty war has on a soldier, especially those with an average age of 19...
Audience whooping? You can't stop some patriotic American's, even if they were misguided. This alone does not make it a bad film. You saw it in the states then I guess?
As for most of the cast being on LSD and (shock) alcohol. Well, find me a film star/celeb who doesn't do one of these. If the actors were on LSD, then it can be considered method acting as drug use amongst soldiers was rife. Comparing this fact against Schindler's List is a stupid argument.
If you didn't like the film, then fair enough. However, I think the points you made were flawed and a little naive.