The thing that worries me about WASM is this exact conflict between compatibility with ACLs and security. It's like handing over your banking account authorization for every possible financial transaction, even if all you want to do is buy an ice cream cone. In the real world, capabilities based system, (aka a wallet with cash) you hand them a $5 bill, and wait for change.

You mean handing over everything needs to drain your bank account, like a check, instead of handing over a number that can be used to deposit money in your account, like the giro system that was developed in Amsterdam.

After seeing the giro system in practice, I couldn't believe that we still use checks...