Your new social/local/mobile app isn't world changing no matter what kind of hustler you are, no matter how much hype you put out, no matter how much money you raise. Anyone can be a capitalist for good or bad whether its exploiting a niche market segment on your own or with a startup.
I believe that regardless of whether you're on your own or do a startup, if your motivation is purely financial you can still do the world great good. Similarly, do-gooders with a grand vision can harm the world. Your stupid little messaging app can connect people from around the world and change the way people communicate (throw in some good crypto and you've done even more good for private comms) or your energy startup that's supposed to change the way we fuel our vehicles and provide clean cheap energy forever can end up doing great harm to the environment or put millions out of jobs as a side effect. These are obviously very hypothetical examples but the point is that there's no "motivation + execution = ethical/unethical success" formula.
There's way too many shades of gray to even be able to consider generalizing like this post does.