Purely as a devil's advocate, what about the fact that Amherst is a (nominally anyway!) private institution, and as such they should be free to educate whomever they feel like. If they wanted to become an all-Black, or all-Jewish or all-whatever institution, who am I to say that they shouldn't?
Of course they do receive, just because of being in the business they are in, a lot of government money, in the form of grants to faculty, and tuition grants and federally assisted loans to students, but still, why should I really care what they do with their spaces, especially if by pursuing these admissions policies they will tend to diminish the quality of their student body on average.
I think they can legally discriminate based on income but not on race, sex, etc. Up to this point we haven't had to have laws restricting employers from hiring based on income, because they've never wanted to. If it became a common practice, however, I think it should be made illegal because children are not responsible for the income level of their parents. Think of the Cultural Revolution in China; income-based reverse discrimination can be very ugly.
Interesting implications here; if Amherst's class distribution is (roughly) 1/4 "URMs" (underrepresented minorities), 1/4 athletes, 1/4 alumni children and 1/4 applicants who have nothing going for them but hard work and brains...it's actually 1/4 upper-class URMs, 1/4 upper-class athletes, etc.
Full disclosure: my daughter was wait-listed by Amherst, I believe Amherst's wait-list is larger than the actual class size, and maybe 5-10 get accepted from the list on a good year.