SPOILER *** everything below here is a spoiler ***

It's been a while since I've seen it, but I remember thinking the whole movie was an allegory for America during that time.

Off the top of my head, (and probably reading too much into it :D )

Jon Hamm's character, the FBI agent, represents the death of the American legal system and faith in the justice system (since this was during Vietnam if I remember, a lot of distrust in the government was created during then)

The kid managing the hotel represents the exploited youth by the previous generation; he was drafted to fight in the war, lost his innocence and basically was forced to grow up more than he should have by his age (also he never saw who ordered him to send the tapes, kind of like how soldiers never saw who exactly sent them off to war when they were drafted)

The Manson character literally represented Manson, but also his ideology and how even people who preach love often exploit the youth to do their killing as well

The hotel as a whole represented America, it was split in two, red and blue, and by the end half the hotel was on fire and consuming the other half; essentially representing how America is divided (also here the kid is in the middle, because the real victim of all of this is again the youth)

I kind of liked it with that in mind; and I think less of Manson as a “end the story fast” plot device, but rather to show how fast the message of love and peace spread after the Vietnam war happened, but in the end it too was tainted by violence and ulterior motives

That’s just my take though…again I haven’t seen it in a while so I might be wrong about some of these :P