> The assumption that this is inherently sex related is where the issue starts. This is why the discussion shifted from talking about sexuality to talking about gender nearly 20 years ago.

Well it was the parent comment that was linking this to sexuality - Hetronormativity is inherently about sexuality (i.e. Hetro-Normativity - Hetro -> Heterosexual: of, pertaining to, or being a heterosexual person).