Che Guevara, Robespierre, Osama bin Laden - they were all either solidly Middle Class or rich. Most poor kids are too busy trying to survive to pursue utopianism or political power fantasies, or they lack the access to radicalizing education. There's the issue of jealousy as well. Radicals are the angry middle children of history who know that they'll never reach the top of the food chain and become CEOs or state governors via hard work and intelligence. But joining a radical movement and tearing down society is a great way to reshuffle the cards and craft a new society where the radicals will be seen as the arbiters of morality. It's like when radical feminists try to tear down society to create a world where they'll be considered more good-looking.
Poorer people might be reticent to shake up the status quo, because they know what it's like to live in a world without basic resources, but rich/middle class kids will happily tear things up, because they've never known hunger or homelessness, and they may feel guilty over their good fortune.
Chris McCandless might have been naive and shortsighted, but at least his guilt over his family's wealth led him to hurt mostly himself. He didn't feel the need to tear up society as a whole or attack people with bike locks because he wanted things to go his way or else.