The argument that Xenon made is that we shouldn't allow people to pay a premium to be able skip the line when voting, or completing jury duty, and hence we also shouldn't allow people to skip the line to get through security at an airport.

Those are 2 very different concepts.  The examples he gave are fundamental rights/obligations for every citizen and every citizen should be treated equally with those.  Flying is not a fundamental right and hence is subject to basic laws of economics, one of which is the willingness to pay, and there shouldn't be an issue with providing a service that people are willing to pay for.