I'm willing to concede that an "extremely sheltered" heterosexual person wouldn't know much about the other sex's genitals. The posthumously famous outsider artist Henry Darger drew girls with dicks because he had one himself, never saw a woman's naughty bits, and never had a reason to suspect they're different.

(But there's more to being a woman that a vag that men and other women are attracted to and trans-identified men will never have. And in a civilized society, people who grew up "extremely sheltered" will likely have other issues that'd render them incapable of giving consent before a social worker intervention.)

Gay people, though? We have our own bodies for reference.