Entropy is constantly grinding away and people need a great deal of reliable maintenance. If some large majority of people weren't contributing to the human race, we wouldn't be here.
When I say "more good than harm", I mean something undramatic. By definition, the vast majority of people and actions aren't exceptional. What people do for themselves counts--if you think that doesn't matter, contemplate how much has to be done for someone who's incapacitated. Just turning yourself over in bed is doing a little bit for the great human enterprise.
Furthermore, most of that good isn't heroic. Getting yourself hurt much while helping out has to be unusual, or again, the human race doesn't make it.
I'm talking about net advantage--many and perhaps most of the people who are doing more good than harm aren't necessarily doing well in all areas of their lives. They might be really good with their families, but useless or mildly negative at work, or perhaps the other way around.
The reason I think all this is worth saying is that I see all too much punditry to the effect that a great many people are just awful. They waste resources, they're irresponsible, they're vicious, they don't pay enough attention to politics and when they do at least half of them are wrong, and they bring too many items into the express checkout line.
There's certainly plenty that could be better, but I think having some respect for what's already somewhat good is easier on the nerves, more based in truth than general condemnation, and less likely to have unintended consequences. It's even possible that epople are more apt to hear advice from someone who doesn't seem to hate them.
Addendum: It can still be more good than harm even if you get paid for doing it. Or even if you get paid well for doing it.