The do-gooders have a reputation for being arrogant — Ilya B Shambat
"Do-gooder" isn't conventionally used for "people who are doing things that one feels are good or worthwhile."
"Do-gooder" conventionally has negative connotations. Do-gooders may be moralizers (in the "self-righteous" sense), they're typically seen as naive meddlers, etc. — Terrapin Station
It has negative connotations, but often unjustified. For instance people have criticised environmentalists and anti-slavery campaigners as 'do-gooders'.
The term is often used by people who have a vested interest in the continuance of a socially harmful practice to try to delegitimise those seeking to end the practice. — andrewk
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