Because you're a decent person. Or, put another way, if you choose to disregard the social contract, you show your lack of quality of character. Either way, it's still a choice and not forced upon people by their circumstances.
“You have nothing, sure, but you still better participate in this social contract that has actually offered you no security or even basic shelter, else we give you even less nothing.” Like... why? Why would that person care? It's called the social contract, not the social religion. A contract has terms that are supposed to be fulfilled by both parties. If one party isn't holding up their end, why would the other?
If your antisocial protagonist chooses to destroy something then he or she is not "giving the finger to the man" or anything like that. He or she is making life worse for other people, most likely normal people who have not done anything whatsoever to ruin the life of your poor widdle antisocial hero. Meanwhile, the billionaires will not be affected much.