It's actually a completely different issue than the ones you've thought of, at a different level -- my issue is that the prefix "hetero" has a useful meaning apart from its use in "heterosexual", just as "homo" has a useful meaning apart from its use in "homosexual". The word "heteronormativity", when used to mean "heterosexual normativity", implies that "hetero" is just short for "heterosexual", and risks losing the meaning of useful words like "heterogeneous", etc.