The quote itself was literally not a metaphor: “Now I actually want to go a step farther, but I realize the president is a kind-hearted man and a good man. I’d actually like to go back to the old times of Tudor England, I’d put the heads on pikes, right, I’d put them at the two corners of the White House as a warning to federal bureaucrats. You either get with the program or you’re gone – time to stop playing games.”

Now, you can argue that this was irony, sure. In the real world, if Bannon isn't delusional, we don't do that and it won't happen. But it's not a metaphor. The word "actually" tells you that right at the start. He is saying, literally, what he would like to do.

And that's awful, and shameful, and if anyone who wasn't on your team said it you'd be screaming (c.f. Kathy Griffin and the severed head -- which was a metaphor!).

No one is being expelled from society.