This week Amherst College announced that it was ending the use of legacy preferences in its admissions process. Its president, Biddy Martin, acknowledged that providing an advantage to applicants who are the children of alumni “inadvertently limits educational opportunity.” When incredibly wealthy, highly selective colleges such as Amherst (endowment: $3.7 billion; admission rate: 8 percent) make an announcement like this, it’s tempting to pour a bucket of cold water on the self-congratulatory fireworks they’re lighting for themselves. That should not happen this time.Still, the temptation is real.