Libertarians are not some homogenous block. A lot of diversity of opinion, never fair to judge a group by just the ones you don’t like or do like. (Every group has people on both ends, and you’ll be able to see what you want to see)
Me personally would be thrilled if the US constitution was actually followed. (A far improvement in boundaries to governance than exists now)
We can see in practice that even the most simple and clear frameworks will bend and break if enough people in society want it to or are ambivalent to its bending. (The difference between societal law and political legislation, read Hayek)
So fixing that isn’t about electing the right politicians as people who win races are more a reflection of the electorate than someone who changes it. (Ron Paul changed the electorate through education, Amash and Rand are the signals of success of that education)
It’s not a matter of convincing people that the constitution wasn’t meant to be bent and broken the way it has but making it clear why these distortions are to societies detriment while still acknowledging people’s concerns that lend them to be ok with these distortions.
This is why finding and creating market mechanisms that can provide people broadly more certainty in for-profit models is so important in creating the environment where expectations can change so that the constitution or equally/greater limited frameworks can thrive.