Tyler Cowen offers several reasons why he decided not to send in a saliva sample to 23andMe:

1. I thought there is option value and I can always do a test later, for a better and more accurate service. (I hadn’t thought of the FDA shutting the whole thing down, but still I expect the service will return in some manner, if only under another corporate banner or from overseas.)
2. I thought the “worry cost” of negative information would exceed the benefit of whatever specific preventive measures I might take. Most useful ex ante preventive measures, such as diet and exercise, are fairly general in their application and I didn’t think there was likely much to be learned about specific measures for specific potential maladies. And here is an interesting short piece on the likelihood of false negatives.
3. One might take more preventive measures with one’s ex ante and more uncertain knowledge than with one’s ex post and more certain knowledge. For instance an absence of negative information might have encouraged me to slack on exercise, to the detriment of my eventual health outcomes.
4. I wouldn’t describe privacy concerns as my major worry, but at the margin still they counted for something. I felt eventually this service would prove equivalent to making my genome public information, via something called GenomeLeaks or the like. Why do that without having a better sense of its longer-run implications?

23andMe held a sale a long time ago, and I sent in a saliva sample. I can attest to Tyler's second point. Opening my test results for things like my chances of getting Parkinson's Disease was terrifying, and it's not clear how accurate the results are.

It's disheartening how much of life's happiness depends on ignorance or self-deception, but even though 23andMe forces you to read and agree to a waiver that lays out all the uncertainty inherent in its current test results, it's likely that test results indicating a highly elevated risk of Parkinson's or some other fatal condition would have haunted me the rest of my life.