My understanding is that Discourse closely follows “don’t ask, don’t tell”.
That is, unless a forum adds a custom user field requiring personal information there is no obligation to provide it.
And even then, except for a valid email address what a member enters can range from entirely fictitious to entirely factual.
After reading this
I’m wondering if making the various profile settings more clear as to who can see them might help.
eg.
this info can be seen by all members
this by only you and Staff