Becoming a public benefit corporation does not make you the good guys, but it does stop investors suing you for pursuing your stated purpose.

It doesn't guarantee that you're the good guys. Okay? Just writing it down doesn't do that much. But it does solve one very specific problem, which is if someone one day sues you saying you breached your fiduciary duty to investors, you could say, "Nope, investors agreed that this is our purpose to do this thing.