Mailboxes are also "randomly out on the road" and can "easily be tampered with or set on fire".
People can blow up a mailbox if they're really sufficiently motivated to do so. People can break open an ATM machine and steal money if they're really sufficiently motivated to do so. People can get a weapon and shoot you in the head if they're really sufficiently motivated to do so. If a crazy person is sufficiently motivated to do a crazy thing, then they can do so. That's not really a sufficient argument against civilization existing.