It very well may depend on the location as LCS previously stated. Most of the members who attended the (several) meetings where I was present were very clearly liberals. Obnoxious, “in your face” liberals. It’s one of the reasons my husband and I stopped going to the meetings.
My experience is in New England, and the members there were distinctly of the impression that libertarianism was widely represented throughout Mensa.
But you have my sympathies either way!