I think you're exactly right here.. others may talk about a slippery road to restriction of free speech but I think societies are right to be more concerned about a slide into the kind of depravity that is typically portrayed as dystopian. I'm very comfortable with throwing the book at this guy and destroying the footage, just as comfortable as I would be if it were child pornography or any other non-consensual act.
I think we all instinctively know what the essence of free speech is and it isn't this. I'm absolutely sure that if the Framers could have envisaged such a situation they would have specifically put it outside the bounds of protected forms of expression.
And.. on a sidenote: You mentioned brutal executions in England. The very term 'cruel and unusual punshment' originates in the English Bill of Rights (http://en.wikipedia.org/wiki/English_Bill_of_Rights) passed in 1689. We've only hung people since then (although there was an unfortunate incident involving some Catholics in 1746).