You line up the list of virtuous things (curing AIDS, feeding poor people) and the list of valuable things (Ruby on Rails programmers, inanimate chunks of metal) and discover that they just don't line up. At all.
Ruby on Rails developers are scarce and valuable just because there still aren't a whole lot of them, and because they can crank out CRUD apps (which are just data collection apparatuses) more quickly and efficiently than anyone has been able to before. Once someone invents an even faster/more automated way to design and deploy a data-collection tool than RoR (which might be just a future version of RoR), then that will be the next big thing for a while.
Ruby on Rails developers are scarce and valuable just because there still aren't a whole lot of them, and because they can crank out CRUD apps (which are just data collection apparatuses) more quickly and efficiently than anyone has been able to before. Once someone invents an even faster/more automated way to design and deploy a data-collection tool than RoR (which might be just a future version of RoR), then that will be the next big thing for a while.