Why is "do-gooder" a slam? The world needs more do-gooders. There's a heck of a lot of good in need of doing.
True, but the do-gooders aren't the ones to do it. I use the term as meaning one who conspicuously purports to do good, especially when that "good" turns out to be not so good after all. E.g., pro bono
work on behalf of serial criminals, deadbeat tenants, and a lot of what portrays itself as "environmental activism." I'll take the silent strivers whose work really benefits society overall, not just certain politically correct portions of it.
See, Google definition: "a well-meaning but unrealistic or interfering philanthropist or reformer."