I don't think that's a very good analogy. It's more like sharing back everything you did to enhance the free pencil sharpener, so the whole project evolves even faster with everyone's enhancements.

I think both GPL and MIT have their place in the open source world. If you want to build something long-term and you want everyone to contribute, then use GPL. If you just care about jumpstarting a solution to a problem, and if you're satisfied if they only use your basic solution at the very least, then use MIT.