Agreed. Not sure why people are downvoting you. It blows my mind every time I think, "I wonder how <some program> works?" and I'm able to just "apt-get source some_program" and check it out.

Working with Linux and having the source (and the ability to change it) for entire stack all the way down to and including the kernel is liberating. As a programmer it feels like the entire world is open to me.

I guess that's GNU's dream brought to life, really.