Admittedly I only fly one to two times per month, but I find myself on a flight with a support animal only about twice a year.
I have never seen one break loose and bite anyone, defecate in the aisle, spread a bad odor, or cause someone to suffer an anaphylactic response.
Is it really such a problem? Is the concern here from busybodies who are just interested in finding a problem where perhaps one doesn't exist?

Furthermore, are any of the respondents trained mental health professionals? I understand that you might not understand how an emotional support animal works, but I bet you also don't know how hemodialysis works. Does that render them both worthless?