Actually this movie isn't all that bad. It's fun and certainly not to be taken seriously. I recall an interview with Milius where he explains that he based this movie on the games he used to play as a kid. Apparently many in USA felt a genuine fear of an invasion back then (whenever that was).
That aside, the movie is playful and the villains range from faceless soldiers to really clever counter-insurgency experts .
OK, so teenage kids are the main protagonists. Big deal. The action is neat even though the FX are slightly weak my modern standards.
And besides, who's to say that USAnians won't fight as hard as any Viet Cong or Mujahedin when their nation is invaded by a foreign power? Frankly, I think they would. Politics aside, I actually think that if this move was redone today, it would reall be way worse than the original...
See it. Don't take it too seriously. Eat popcorn. Have fun.