With such amount of money you have power to change not only your life, not only life of your family, neighbourhood, city but whole region/ country.
Its funny to see hoow many people say that if they had the money in questions they'll not only think about themselves but about saving/changing the world. I believe this thought would not longer exist once presented with the money because just then you realize how much more you need as an individual - its just being human!
People are different, not everyone thinks the way you do, lots of people don't make a lot but they still try and make an impact on the society, trying to "save/ change the world", so if one of such persons would get $$$ why would they change their behaviour?
There is a saying that you can't buy friends - but I think there are exceptions, if you do a lot of good things for people around you, you can "buy" friendship not only from them but also from other people who see your good deeds. And a lot people want to be popular, they want to be celebrities - so by "saving the world" they are buying something, just not a material thing.
And one more thing, by "saving/ changing the world" you can still make money, for example you may do something in better way than other companies - e.g. in the fields of ecology, fair trade etc.