They were probably serious. Extreme libertarianism (as well as many other ideologies) judges the terminal value of a law based on the law alone; the system by which the laws get made (absolute democracy? constitutionally-limited democracy? benevolent dictator?) is then just a means toward that end. The belief that a financially-limited franchise would infringe less on liberty might still be wrong, but it's not inherently self-contradictory.

We tend to lump ideas like "freedom", "democracy", and "self-government" into a big halo effect box of happiness, despite there being serious historical and modern conflicts between any pair of them. If a majority of people desire to ban flag-burning, under what conditions is it right for a minority to ignore that desire? If a large majority of people in some locality want strict enforcement of a particular religion's edicts there, does it matter if they're greatly outnumbered by non-locals who disagree? Does the answer to the previous question change if I insert "don't" before the word want?