He mentions how society is at its core a contract on how to engage with one another. Everything we do is in some form conforming to that contract and when this contract is violated (like the stores being looted and vandalized), it angers you.
However, to the people who're really affected by this issue at the very bottom of the society - they feel they're being ripped off in the contract and are being cheated every single day. After a breaking point they can feel like they don't really have to adhere to the contract anymore themselves when no one else sticks to it in their oppressed world.
PS - Please note, he's obviously not justifying the lootings, mainly tries to make sense of it and how we got to where we are right now.
but it's because they are the status quo, and they define what's looting or not. i'm not in favor of stealing and violence, particularly because the ones getting stolen from are at the bottom as well, but it sure seems those at the top sure live in a different society and under different rules that conveniently favor their form of "looting".