Is it rude to never tell a partner about my mental disorders?

I have some highly stigmatized disorders. I will be going to therapy and I am on meds. Why would I have to tell someone? Especially when people go “I will never date another person with ____ ever again.”
Is it rude for me to then not tell them I have that disorder until we are married or something?

I am never telling the person I am with about my mental illnesses, so this isn’t me asking what I should do. They can learn that about me once we are seriously committed/married. I am just curious if it is rude.