Oh, I fully understand WHY they misuse GENDER; it is because instead of saying SEXUAL INTERCOURSE, they simply say SEX. Thus, a confusion may arise. There was the old joke about the question on forms:
SEX ________
& the guy writes 'occasionally' rather than MALE or FEMALE.
It is just like FRENCH FRIED POTATOES (1894); when was the last time you heard that term?
1st, it was shortened to FRENCH FRIES (1918), but they do not even say that anymore! The verb FRY became a noun, FRIES! But the average dictionary goes into the ETYMOLOGY of words very briefly, if at all.
I learned formal grammar by setting my old WORD PERFECT to its highest mark, to formal grammar. I had a ton of trouble with the active Vs. passive sentences, & I still have trouble with fragments. I well know that educated people use colloquial English, I worked with electrical engineers and computer scientists, they all used rather poor grammar.
Back to GENDER, my ETYMOLOGY dictionary says:
Probably about 1350, grammatical class referring to nouns and pronouns; later referring to verbs (about 1450).
It then goes on, to clarify these meanings, but says nothing about its being a synonym for SEX, or anything about the controversy. However, my thesaurus Rex has this:
418.1 SEX
Nouns 1. sex, kind, persuasion [joc.]; gender [coll. exc. gram.],
'col.' = colloquial.