a puritan
Examples
A puritan is a person who pours righteous indignation into the wrong things.
[Of Guizot] A Puritan born in France by mistake.
In the United States there's a Puritan ethic and a mythology of success. He who is successful is good. In Latin countries, in Catholic countries, a successful person is a sinner.
Art is so wonderfully irrational, exuberantly pointless, but necessary all the same. Pointless and yet necessary, that's hard for a puritan to understand.
If you have beautiful knees, show your knees. I'm not a puritan. I love skin.
I was raised not so much in a puritan environment, but for the most part, a pretty healthy one.