This idea really represents a huge misunderstanding of what kinds of things actually drive political disagreement.
The whole point of PitMK is that political disagreement puts us in a situation where our biases are even less under control than usual. DNA testing that shows one candidate to be likely (but not certain) to be smarter than the other one isn't going to do a damn thing about that.
The media spent a lot of time discussing Palin's intelligence presumably because many voters cared about it.
I agree that "political disagreement puts us in a situation where our biases are even less under control than usual" but additional information could reduce these biases. The situation under PitMK isn't hopeless.
Lots of Republicans thought that Bill Clinton was a sociopath. Let's say he was. PitMK would make it challenging for Democrats to see this. But if an analysis of Clinton's genes showed that a child born with his genes had a 70% chance of being a sociopath then I doubt Clinton would have won the Democratic party nomination.
I wrote an article for h+ predicting that the rapid fall in the cost of gene sequencing will allow U.S. voters to learn much about presidential candidates' DNA. The candidates won't be able to stop this because:
DNA analysis has a decent chance of reducing political bias by providing objective information about candidates. If, for example, 70% of the variation in human intelligence is determined by identified genes then DNA analysis would reduce disagreements among informed voters over a candidate's intelligence.