What would be a better way to express his point?

I see this brought up a lot, and I get it: we SHOULD be able to treat everybody equally regardless of the bits between their legs, but we haven't gotten there yet.

I think it's counterproductive to be pedantic about language when it's serving a purpose and not hurting anyone. If someone brings up a better way to express this type of thing, then I'll be in total agreement, but I haven't found a better way to do so using the english language.

You cannot find a better a better sentence than one starting with "Women must also"?

How about: "Some people, regardless of gender, can perpetuate or reinforce gender roles through speech, action or inaction."

"Some people should be willing to give up traditional gender roles."

I think you're abstracting this a little too much. The sentence you constructed would be useful to describe this in general, but in this case PuffinBlue is talking about a specific case where this language isn't entirely useful.

I agree that that type of language should be used in general (and I make a concerted effort to use it, even in my native tongue where sex is strongly denoted), but IMHO it's useless when describing specific scenarios.