Here’s my take. The whole movie is a parable, and every character is like an archetype. Nicholson’s character shared their ideals, but unlike Hopper and Fonda he wasn’t dealing drugs to fund his own pursuit of happiness. He might have been a drunk, but he wasn’t cheating.
So his death is the “death of innocence”. His death represents the death of the childlike idealism of that generation, as they become jaded and hedonistic.
I hate movies that have to be some kind of ‘message’.
As Sam Goldwyn once quipped, “If you want to send a message, use Western Union.”................