In their thread about the dangers of letting people mark their gender as non-binary on their passports, Fair Play For Women mentioned that one of the dangers is that it would allow people to "opt out of sex-based rules and responsibilities".
twitter.com/fairplaywomen/status/1414150978782253059
Some in replies and quote tweets remarked that it just sounds like gender roles.
So, what "sex-based rules and responsibilities" is this referring to, exactly?