"Humanitarian" work within ML?

I am a graduate student in computer science with a mathematical background. I am considering what to write about for my master's thesis, knowing that my choice will determine to some extent what I'll do in the future. A topic within ML is possible. I came to this subreddit looking for more information and browsing the top posts I read interesting AMAs with some leaders in the field. I felt like the one with Yann Lecun was particularly interesting - but in my opinion it is disheartening to learn that a man like him is working for Facebook. A part of the post here by Max Welling (commenting on the controversy when Mark Zuckerberg visited the NIPS conference) expressed my thoughts exactly:

Is it desirable that big companies lure our best students away to improve ad-placement, where they could also have contributed to curing some of the horrible diseases that plague mankind? Perhaps not, but people have the right to make their own decisions.

Expanding on this: what opportunities do ML researchers have when it comes to things like "curing horrible diseases" or just doing work that is beneficial to humanity in some tangible way? Is anyone here working doing that kind of work? Can one expect to be able to enter that kind of a career after graduating (from a PhD program or otherwise)?

Thanks for any input.