Brands system doesn't prevent double-spends, it merely detects them and identifies the culprit. In a traditional bank system your bank will then debit your account a second time, and they have the contractual authority to charge you for an overdraft, and ultimately take you to court or send in the debt collectors if you don't pay off your debt. To do this in an online context you'll need to establish some sort of reputation system to ensure cheaters can't move between banks.

Ultimately, it needs to be backed by system with a monetary policy, since whatever fraction of double-spending you cannot prevent effectively causes inflation of the money supply.