I think the big contention is yet-another "optional" feature you cannot rely on when C++ security record is so-so with regards to memory safety, and if you for "elegance" put predicates for such into contracts.. it can all go out the window even if you intended for it to be strict.

I think defaulting all assertions to enforce would've been better with an optional soft modifier (ie "soft pre(foo)" ), as it is now it's just always assert in a trenchcoat.