The problem is "Greatness Cannot Be Planned". There are not many cases where someone ambitious sets out to make the world a better place in a very direct way, who actually accomplished that, because of deceptive objectives. Nobody would have predicted that something as frivolous as PC gaming would lead to the AI boom we're having now, but it did. In many ways, John Carmack did more good by kickstarting the PC graphics race than any morally ambitious do-gooder has ever done. There is one notable exception, and that is Elon Musk. He attacked two extremely difficult industries head on armed only with $100m and grandiose plans, yet somehow made it work by shear force of will. Difficult to replicate, and of course we all hate him now.

Better probably to do what you find interesting, and maybe it will lead to greatness. If it didn't at least you did something interesting.