Make it easy to do but also easy to undo anything, while also having a very large amount of transparency in the system so any "bad actor" can be dealt with swiftly.

That seems to work for the banking system, where any malicious transactions are easily "reversed" (often just reversed on one side actually, 'paid for' by insurance / banks) and a large amount of auditing which makes it possible to clamp down on the bad actors quickly.

Abusing the system then no longer becomes a technical challenge so it removes the possibility that someone with the right technical prowess can "break" the system. Robbing a bank is the easiest thing in the world, just walk in and ask for money, it's getting away with it that's difficult.

I work for a bank on blockchain projects. It's almost never this simple. You'd be suprised how much banking is paper based right now for the simple reason that no party wants a central solution controlled by any other party.

A lot of these companies are doing experiments using private blockchains (like the private ethereum network linked in OP). However depending on how much you trust the "other" parties allowed to mine (or sign blocks), you might still have the risk where one or more conspire against you and 51% attack you. Periodically putting a blockheader of your private chain into a public blockchain would be a great solution to this, as pulling off a 51% attack on bitcoin is rather hard.