I think it's clear that people aren't, nor should they be expected to be, completely selfless in all their reasons for wanting to do something like volunteering in India or Africa. After all, if all you want is to be as selfless as possible, aren't you simply pursuing your own desires for self-fulfillment and satisfaction? I think it's an irrelevant argument.
A lot of people really value the opportunity to live in another, radically different culture to gain perspective or simply because they like it. Some people may not want to do some drunken American kid-filled semester at sea or study abroad. In their mind, they might rather do something, even if it's only a token, to serve the communities that they are using, to some extent, for their own personal development. I agree that in the long term, it's way too easy for people to run off and "save" Africa while ignoring the needs of communities at home. I also feel the emphasis needs to shift towards training and retention (countering the brain drain) of native health professionals in developing nations, rather than the somewhat 'colonial' practice of flying in western doctors for brief stints. But regardless, if someone has a drive to travel like this, it will be a lot more difficult to do it in the future, even with opportunities like MSF (depending on specialty, patients may always be booked months ahead of time and it won't be easy to take off for a few months). So if you have the opportunity, I say go for it now!