"You do‘’ refers to emphasis tone, you think it should be "Do you realise"right? That's simple question tone.

"You do realize" is almost the same as "Do you realize" except that we are expressing hope or expectation that the person already knows something (that it's a completely insane request) - even though we are not completely sure. The meaning, however, is the same. "You do realize" in this case is also something like a mild scold. It's very good that you pick up on these nuances! :D