@trust is an encapsulation method, not an escape

[via Digitalmars-d]

And I'll add this:

Please do not turn the compiler into a inadequate verification 
tool. The compiler should do what it can do well, but what it 
cannot do it should not do at all and leave to an external 
verification tool.

@trusted basically tells the compiler "this is beyond your 
capability so we left it to someone else".

Third parties should be able to provide incrementally improved 
verification tools, for various purposes, without mandating 
language or compiler changes.

So what you want from the language is simple clean semantics and 
reasonable best practice annotations for verification that can be 
extended based on the needs in a particular environment.