I'm talking about the efforts to change the definition of "gender" from referring to biological sex (biologically-determined physical attributes: chromosomes, genitals, hormones, etc., which for most people line up into "male" or "female", although intersex people exist) to referring to how you dress, act, or just personally identify.

Background:

According to the Online Etymology Dictionary, "gender" for biological sex goes back to the 1400s (and it became the word for human biological sex in the 1900s), while the newer use of "gender" is first attested in 1963.

The "male-or-female sex" sense is attested in English from early 15c. As sex (n.) took on erotic qualities in 20c., gender came to be the usual English word for "sex of a human being," in which use it was at first regarded as colloquial or humorous. Later often in feminist writing with reference to social attributes as much as biological qualities; this sense first attested 1963.

Wiktionary backs this up:

Since the 1960s, it is increasingly common—particularly in academic contexts—to distinguish between sex and gender, the former being taken as inherent biological distinctions and the latter as constructed social and cultural ones.

An example of the newer definition, focusing on roles and behaviour (from this subreddit, not providing a link because I don't want to pick on the person):

Since the '70s, it has been widely accepted that gender is more of a social construct and differs from sex in that it also encompasses roles, or behaviours. As in the saying, typical gender roles.

Another example, focusing on self-identification:

Any man's manhood is valid regardless of what kind of body parts he has, or what gender he was assigned at birth. Having or wanting to have a penis are not what makes someone a man. Only identifying as a man makes someone a man. [http://nonbinary.org/wiki/Binary_genders#Male]

First thought: If we're going to change the definition of "gender", we should be explicit about it.

I think the vast majority of people use the older definition of gender. When a person using the newer definition addresses it, from my experience they almost always say something like "you don't understand, actually gender means this". This portrays it as if the new definition of gender is a scientific discovery that the person being addressed just doesn't understand, but really it's just a difference in definition.

I think it's more intellectually honest to be explicit that there's an older definition and a newer definition and they think that the newer definition is better. The only example of someone doing this that I can think of is Scott Alexander's Slate Star Codex article "The Categories Were Made for Man, not Man for the Categories", which makes it explicit and makes a good argument.

Second thought: I can't help thinking that the intention behind changing the definition of gender is not to add a concept to care about but to erase biological sex as something that people care about.

This is for three reasons:

1. First, they just happened to pick words that were already used for biological sex ("gender", "man", "woman"). If we're talking about gender roles, appearance, and behaviour, why not just make it "I identify as masculine (or feminine)"? Why appropriate the word for biological sex and make it "I identify as a man (or a woman)"?

2. Second, although it's said that sex (male/female) and gender (man/woman) are separate, people who advocate this separation seem to want "gender" to be the only valid thing to care about. For example, in the transgender bathroom debate, a store-owner could theoretically accept this sex-gender distinction and say "I recognize your gender identity as whatever it is you say, but our bathrooms are segregated based on sex, not gender", but that would be seen as wrong.

3. Third, the words that are supposed to be left over to refer to biological sex—"male" and "female"—are very often used for this new definition of gender anyway ("Anyone with a male gender identity is male: he is a man or boy."). That's not making a distinction between sex and "gender", it's just changing everything to the new definition of gender.

Any thoughts on my thoughts?