I believe your son has a right to identify himself in any way he wishes to. Keep in mind that your son (I assume, correct me if I am wrong) was born in a different time than Obama. In 1961, most whites and blacks disapproved of interracial unions, today most are accepting of them and their offspring.
You're half right. My son was born in 2000. But no, when the time comes, he will not have the right "to identify himself in any way he wishes to." If I ever hear him identify me out of who he is, I'll kick his butt, even if I'm 80 by that time. People don't have the right to identify themselves dishonestly.
You are also right. Looking at the scope of social history, I wonder why people are not more amazed at how wonderful and fast America has changed.