Does "I'm not X because of Y" mean "I am X, but Y isn't the reason" or "I'm not X, and Y is the reason"? Perhaps in spoken form one could distinguish by inflection; I'd think that the first meaning would be expressed with a rising inflection (anticipating giving the real reason).
Signed,
Puzzled
P.S. I still recall a time that a good friend of mine from down south saw an interracial couple (black man, white woman) up here (in Iowa) when we were at a restaurant. He asked me whether it was a common occurrence. (I had to say that I'd seen such couples a few times, but hadn't really been keeping count. Like other respondents here, I haven't personally happened across an interracial couple in which the woman is black and the man white.)