I don't necessarily buy into market self-regulation (as I believe this to be the primary reason our government is bought and paid for), but the principle is internally consistent. Libertarians believe that the the markets will self-regulate. If one company promises not to sell your information, it should give them a competitive advantage in a market where people value privacy. In a perfect libertarian world, that might be a working strategy. However, in a world with monopolies that can leverage the power of the government to restrict competition and corner the market, voting along ideological lines is not practical.
While Rand Paul might be consistent in his ideology, corporations will take advantage of his idealism. He will never have the power to remove the monopolies. Therefore, they can get his vote when it benefits them (as long as they mask it in a libertarian ideal), and ignore him when they are looking to quash their competition. He is either too principled or short-sighted to see this.
This is one of my fundamental issues with libertarians. You have to work on the big issues first (welfare, both in individual and corporate forms, break up monopolies, and government overreach), before you can work on deregulating in other areas.
To extrapolate though, you also have to allow terrible (and preventable) tragedies, like Flint, with no regulation.