I think you are being unfair! What is meant in the original post is that no person is immune to mental illness by virtue of being a member of a group or set of persons. That mental illness is a human problem, not a problem of only certain groups of persons. The sane are susceptible to the threat of mental illness; and that is why they keep their distance - a reason for (what is seen as) stigmatization.
As for your disagreement with Freud: are you sure? After all, you believe that you're sane and that is not what held you in a psychiatric unit during January and early February this year!