We care because if there's a reasonable degree of it we can tell ourselves we don't have a rigid hereditary class system which, at least once a upon a time, even most conservatives in this country didn't claim to be fond of. It's all part of the whole 'if you work hard you can succeed' mythos of our country. If that part isn't true, then most of the rest of it is bullshit too. That is, we have a society where the fundamental determinant of your success is who your parents happen to be, and there isn't really anything much individuals can do about that.
