There was a proposal to do just that in our DIP (D improvement proposal) pipeline that nearly made it but it (probably correctly) received enormous backlash.

However, if you use @safe (that's the attribute) the compiler will hard-error if you call any code that you use that isn't explicitly also either @safe or @trusted.

There is also DIP1000 and DIP1021 which both loosen @safe semantics to perform semantic analysis to allow safe memory behaviour (A small borrow checker in effect, this will hopefully be bigger soon).