I can understand enthusiasm, and even sometimes zealotry. But please, before you hijack the library computers and arbitrarily install Ubuntu on them, please, please think twice.
You’re going to infuriate the librarians. You’re going to alienate the staff and the clientele. And you’re going to confuse and bewilder a lot of people that might not even know you. Who’s left that will listen to you explain why it’s better?
And do you really want everyone’s first experience with Linux to be such a hatefest? This is about convincing people that Linux is a better idea. Not force-feeding them a new way of doing things.
It’s just bad karma all around.