One way I look at it is the beheadings are seen more or less as a legitimate way of execution in the Middle East, so a lot of detractors wanting Jordan out of the conflict at home did not view the murders as anything out of the normal killing wise.
However, I feel that setting fire to a caged prisoner is a different entity altogether and something that even Jordanian hard line Muslims are offended by, that far from acting as a catalyst to cause further dissent at home in Jordan may have just done the opposite and cemented a will to see IS destroyed.