That DNA evidence that could exonerate you? You don't have a right to it, says the US Supreme Court.

Actually, not being a lawyer or constitutional scholar, I don't know what kinds of evidence you have a constitutional right to when you go on trial, so I'm not going to comment on the correctness of the decision. But legal scholarship aside, two things are obvious:

1) When we try someone for a crime, we want the best, most reliable evidence possible. It's probably reasonably safe to say that most people with at least some wisps of sanity would like our criminal justice system to convict the guilty and acquit the innocent.

2) DNA evidence, (when analyzed and used properly), can be incredibly powerful. The science of forensics is unfortunately a scientific backwater, which needs an influx of talented researchers. (Looking for a job while the economy is in the dumps? Try grad school in forensics!) However, DNA evidence can be incredibly powerful, because the hundreds or thousands of base pairs that you can test add up to an irrefutable signal - one orders of magnitude stronger than what you get from fingerprints. Nobody in the world, (not even in your monozygotic twin, apparently) has the same DNA you do, and no subjectivity at all is involved when we really want to distinguish your DNA from that of another person - you just read out the A's, T's, G's, and C's, and they either match or they don't. I can't think of any other physical trait that is equally unambiguous.

So, instead of arguing over whether we should include DNA evidence or not, we should be beefing up the standards for evidence collection and DNA analysis protocols (because, in spite of the potential of DNA evidence, it can be used incorrectly, which of course leads to controversy in court), and then requiring DNA testing to be used in any case where it is available - a prosecutor, who may be more personally invested in getting a conviction, even if it's not an accurate one) should not have any leeway to decline such evidence.

If we ignore DNA, we're willingly turning a blind eye to an extremely informative form of evidence.

DNA Fingerprinting, courtesy of PaleWhaleGail vis the Wikimedia Commons