This seems like a great tool for stalking people; particularly the recursive functionality (for tying identifiers together).
I'm not saying the world is worse-off due to the release of software like this - indeed, you could argue that publishing these sorts of OSINT tools allow folks to take a proactive and protective view of their own information and e.g. make changes to their own profiles/privacy settings.
But the question of ethics seems like something all-too-often glossed over in the infosec world. Software doesn't exist in a vacuum.