Do-gooder

Prohibition in the United States was an unsuccessful attempt by do-gooders to save people from the dangers of alcohol, whether they wanted to be saved or not.

I was hopping along, minding my own business. All of a sudden, up he comes, cures me. One minute I'm a leper with a trade, next minute my livelihood's gone. Not so much as a by-your-leave! “You're cured mate.” Bloody do-gooder.