May or may not

It’s common (but painful, to me at least) to see may or may not used in a sentence. This is poor English, because ‘may’ conveys the idea of possibility by itself: if something may be the case (this newsreader may be drunk; humans may evolve in one of four ways; John Travolta may have molested a man over hamburgers), the simultaneous implication is that it may not. Adding may not to a statement already qualified by may is superfluous.