C-Bug.

[Maddolis]

So that we can use the weapons without knowing that we're gonna be crushed.
Fighting with the c-bug is hard, but it is fun, not only would be be able to have walk weapon duels in world 0, but we'd be able to test out walk weapon skills against sawns and uzis- winning those fights is a fresh change. There are a few smaller reasons, but basically there's no strong reason for it to be disallowed.