The phrase can be used in two contexts, one as a figure of speech. The figure of speech context does NOT have any threats involved.
Now, here is Bannon's statement:
"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."
In this context, Bannon does not seem to use it as a figure of speech, it is a threat - maybe not literally - but a threat nonetheless. That's what's wrong, and why people are angry. Not because they don't like his "ideas".
I've seen as nauseum posts accusing Drumpf and his cohorts of treason, for which the penalty is death, not to mention more recently scads of Twitterers gleefully posting photos of the mutilated corpse of Mussolini and expressing desire for the same to happen to the president and his "collaborators".
It's getting to the point where AOC's recent calls for lists of said collaborators be compiled for harassment and ostracization seem reasonable, as at least she's not calling for their execution.
We could have seen this coming several years ago with calls for violence against "Nazis" (and btw a Nazi is anyone who disagrees with me politically) but big tech looked the other way because they support it.
I'd expect more cogent analysis from the top intellects if HN, but apparently the stereotype is true: "It's acceptable when our side does it".