Don't be the chump who offers the rational middle ground as your opening bid.

I'd say there are at least 2 morals.

First: You don't get what you don't ask for. the other person might really only want a quarter of the cake, but by asking for more than your "fair share" you open the door to allowing them to give you what you want.

Second: By asking for the whole thing, you have placed yourself in a position of power and privilege. The mere act of asking for more implies that you think you deserve it. Someone mentioned posturing in another comment.

Selfishness is a virtue and not a sin as taught and propagated through society, religion and culture.

If you wish to get what you want, you have to use any means possible. And there is nothing wrong in it.

Actually if you look at it that is how most successful people get successful.

Think of your own good first, even if that's not very helpful to the other guy.