Everyone must watch this absolutely awesome video by Richard Stallman on why free software is important. He had a vision in 1983, and over two decades later he is still absolutely dedicated to it.
Among other things, free software promotes learning, because in RMS's words when a student is doing something with a computer, maybe typing a command, he might be curious to understand how it works. Well if he is working on a GNU/Linux box, he will actually be able to do that. This ability is the biggest advantage, because it allows students to study a system under the hoods.