He didn't actually say that, and I'm not sure how it spread. However, he's still a terrible person, and here's the quote yours spawned from: “There is no basis in text, tradition, or even in contemporary practice (if that were enough), for finding in the Constitution a right to demand judicial consideration of newly discovered evidence of innocence brought forward after conviction.” edit: This was originally in reply…
Why is that a terrible quote? Remember, there's a reason that the process and traditions are followed. It helps provide (theoretically) a uniformity of enforcement. In the case of your quote, the exact same mechanism for "evidence found after the trial changes to innocence" is quite possibly used for "evidence found after the trial changes to guilty". It nudges up against double-jeopardy. There are other problems wit…
A slippery slope evidentiary argument that would tend to exonerate is not a concern that it would later be applied to retry or change to guilty a previous acquittal, IMO. The courts have been quite clear on this.