"Of all tyrannies, a tyranny exercised for the good of its victims may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end, for they do so with the approval of their own conscience" -- C.S. Lewis
...and the most dangerous.
Leftists are the contemporary recrudescence of the Puritans. They would love to force smokers to wear scarlet letters, for example. Their furvor in forcing conformity on others matches the most puritannical religious fanaticism.
They would hate this comparison, but, if they had sufficient honest insight, they would see that it is true. Of course, if they were capable of that kind of honesty and insight, they wouldn't be Leftists in the first place.