I think part of sound decision making involves weighing likelihood, risks and rewards.
To me, PKU testing is nothing remotely like an unnecessary C-section or circumcision. Something like a C-section has very clear risks, along with circumcision, hospital births, etc. Many would argue that vaccinations have clear risks and low reward (after a lot of research I chose to vaccinate on just a slightly delayed schedule, but I respect the thought process and cost-benefit analysis of parents who don't vaccinate).
I think that, while the likelihood of having a metabolic disorder is low, the test has virtually no risks and a potentially huge reward. So for me, it's a very easy decision to make. If you're concerned about where the sample ends up, go through a private lab or lobby for change. But don't disregard the test altogether.
As far as the accuracy of the test goes -- in a lot of screening tests, from a public health perspective, what you're trying to do is capture as many positive results as possible while missing as few positive results (false negatives) as possible, for the lowest possible cost -- remember, you're administering this test millions of times per year.
That's why a lot of these general screening tests have a high rate of false positives. Is it ideal? No. But currently it's the best we have. Pap smears also have a high rate of false positives, and many abnormal pap smears fix themselves. Others, if left untreated, go on to cervical cancer. Even though the rate of "false positives" -- in this case, abnormalities that will clear themselves without treatment -- is high, the screening has led to a 75 percent decline in cervical cancer deaths in the last 50 years, by catching those cases that do need treatment. And like the PKU testing, this is a case where early detection can make a huge difference in outcome.
To me, the main difference between Pap smears and PKU testing is that an adult woman should be responsible for making sure she's getting regular pap smears, while a newborn can't make the decision to get tested for a disorder that could leave them profoundly disabled within a year, or non-disabled with dietary restrictions. We as parents have to do that for them.
You keep on saying that you don't want to debate this, but in an open forum, if you start a topic, people are going to respond and they may very well express strongly differing viewpoints from you (hopefully in a respectful manner, since this is MDC.)