An important thing to note is that this is an exception to the rule: you aren't allowed to call someone mentally ill, unless it's based on gender or sexual orientation.
> Mental characteristics, including but not limited to allegations of stupidity, intellectual capacity, and mental illness. [...] We do allow allegations of mental illness or abnormality when based on gender or sexual orientation
Edit: I re-read it and I think you can normally call someone mentally ill if it's not because of a protected characteristic. It's still a targeted cutout to allow transphobia/homophobia specifically. So you can call someone mentally ill for liking pineapple on pizza, or being gay or trans, but not for being black.
https://transparency.meta.com/policies/community-standards/h...
> Do not post: [...]
> - Insults, including those about: [...]
> Mental characteristics, including but not limited to allegations of stupidity, intellectual capacity, and mental illness. [...] We do allow allegations of mental illness or abnormality when based on gender or sexual orientation
Edit: I re-read it and I think you can normally call someone mentally ill if it's not because of a protected characteristic. It's still a targeted cutout to allow transphobia/homophobia specifically. So you can call someone mentally ill for liking pineapple on pizza, or being gay or trans, but not for being black.