There are a billion ways you can split a democratic body in to a majority and minority. We don't give the left handed, orphans, or people whose name starts with F extra voting power because the righties, parent havers, and all the other name start letters could gang up on them. So if being a minority isn't an obvious reason on its own to be given more voting power, then there needs to be more reason to do so for the states, and every time I see this brought up the only defence is that the small states would have a minority of votes.