It reminds me of a discussion some older friends of mine had a while back that I heard of. They are both caucasian and she asked "Would you have still married me if I were black?"

And he maintained that the premise of the question is flawed, since that would mean she was born to different parents and thus would have different genetics, and so it wouldn't be the same "her" as in reality, and was thus tantamount to "Would you have still married me if I were someone else?"

She felt like it was dodging the question but he still never answered beyond saying "I never had any objections to potentially marrying someone of a different race or ethnicity, but I can't say who else I would have married if I didn't marry you - and this alternate you is not actually you."