As stupid and tasteless as it was, to make it into a call for others to cut off his head is specious at best. And that's a key issue in play: the intent of the the message.
You're engaging in weak whataboutism.
One of the major threads of the political discourse is that right wing businesses, representatives and protestors are being treated differently than left wing ones. How would you - even theoretically - make that case without drawing comparisons?
There is little room to argue that if any figure associated with the right was waving a mock severed head around that would be cause for extreme social, business or potentially legal consequences and/or people losing faith in basic civil liberties. There would be panic.
The standards are too visibly different for the gap to be dismissed.
The right wing protestors at the capitol were trying to overturn the results of the democratic process, and were prepared to do so by force.
There's a difference there.
It’s literally the topic of discussion. You could say, two sides of the same coin, but it’s not even really that.
Where do you draw the line for violence and inciteful speech? If you’re willing the draw a different line depending on the policy goals of the person speaking, then you’re taking a political position not a moral one.