Untrue. In fact, the differences are large enough that medications can be indicated for white people and generally less effective in black people, or vice-versa. However, I'm sure you meant that these differences are completely irrelevant for deciding who should be able to marry whom, and I agree completely with that.
Actually, 50 years ago it was remarkably common to say that the differences between whites and black were so large that interracial marriage should be banned, just like you are now saying the differences between men and women are so large that same-sex marriage should be banned (or, if you are not saying this, I'm not sure what your point is). The differences between being black and white have not changed significantly in the last 50 years, but the importance we have attached to those differences has changed. Similarly, I suspect that 50 years from now, the differences between being male and female will seem less relevant in who should be able to marry whom.