In my experience, if someone is defining you negatively, they may be doing it to make themselves feel better about themselves. You can try to explain yourself until you're hoarse, they simply refuse to let you grow out of the box they are confining you to.
So I've learned to just get out - and don't waste time and energy on people like that. Seek out someone who likes to assume the best in people, not the worst. You'll be happier. It's their loss.
If I am reading your question correctly, . . . Have I been stereotyped by an intellectually inferior person in an attempt to justify his/her unfounded position of "moral"/etc. superiority and/or diversity? Yes. As for getting out without being mean? - - - I don't. I adamantly defend the many facets of who I am and merit of my positions. If this includes demonstrating the myopic inferiority of a person attempting to pigeonhole me, so be it. People often accuse me of being nice. I tell them I am not nice. I am fair and honest and generally treat people with empathy and kindness but If anyone attempts to limit the definition of who I am. I am not nice and I believe this is the correct response.
I'm a schizophrenic and I get put in a box all the time by people thinking I'm a psycho or something. My comeback is just to be myself because I seem just like a normal person when I do and it goes against what they think they know about this affliction.