I confess that the thing which bothers me most about liberalism in religion and in politics is that it so rude and boring. It is rude to be always telling people how they are to speak, how they are to be generous, how they are to be just, how they are to be loving. Liberalism is boring because it is never new, rather merely modern and up-to-date. That, maintained St. Thomas, is a moral evil.
Any human act against reason is morally evil. But it is against reason for a man to be a burden to others by giving them no pleasure and by preventing their enjoyment.
Seneca remarked, "Let your behavior be guided by wisdom, so that no one will judge you to be rude or a boor." Now a man lacking cheerfulness and humorous speech is a burden to others since such an individual is not attuned to the moderate mirth of others.
Consequently, this person is morally evil, rude and a bore, as Aristotle says in IV Ethics.
Summa Theologiae, II-II, 168,4, c.
I suppose that religious and political conservatives sin against moderation in mirth, surely the better sin in a 'dark and cheerless' age.