So here's my take: The Right to Dream is about coming together with a group of people and establishing boundaries and then exploring the space within those boundaries with no end in sight other than to explore the world in question. You don't want to win and you don't care about coming out at the end with a good story, what you want is experience and exploration, to come closer to understanding and engaging in a fantasy than you would have ever had if you hadn't jumped into the sandbox.
No one is right or wrong, everyone wants to support everyone else's exploration, but it takes a lot of common ground to do this. Its dangerous, to hand someone your idea for a story or a character, or to invite someone into your vision of your favorite fictional world, and to let them bash around in it with you. They might break something you hold sacred. With no direction, too, play can devolve into strange things, highly personal nooks of dream space, places that only entertain or make sense to anyone but the one dreamer. In the Right to Dream you have to promise not to break anything and not to beckon people to go too deep.
So, thats it, the Right to Dream. Why would you do it. To play in that childlike sense, when in little moments you transcend and emerge through the game into the fiction. Its about wanting to act out in a way that isn't acceptable anywhere else. Its about exploring just how durable your visions are. There are so many reasons and so many reasons to buy into the Right to Dream, but that's my take on it.