I don't think that the notion of crucifixtion was a deliberately cruel death chosen by God as a symbol of his love - it was simpy the common criminals' death at the time. As Lenny Bruce said, if Christ had been executed in modern times, we'd all have little silver electric chairs on chains.
Relaitvely speaking, cruxifixtion is by no means the cruelest death that has been designed by man for his fellow man - read any of the number of books about torture through the ages, and you will see far more inventive, prolonged, sadistic and inhumane ways to kill someone which place crucifiction quite low down on the scale of prolonged suffering.
As far as the crucifiers being people who would 'satisfy a commanding authority' - I think you elevcate their mental processes far above their actual level.
In an occupying army - which Rome was in Palastine, you will always find enough soldiers who regard inflicting pain on their perceived enemies as a fortunate byproduct of their solidering, given that they were able to sell the clothes of the vistim to suplement their salaries.
You only have to be a regular on here to see the vast numbers of people who claim they would pull the leaver / throw the switch in order to demonstrate that their mooral outrage is more outraged than anyone else's. For the record, I think they are full of hot air - it takes a very particular kind of person to take a human life in cold blood, but that is another issue for another debate.
So for your Question - I think executioners throughout the ages have been of a certain type who are able to do the job becuase it needs to be done, and that has nothing to do with being forced into it by another authority. Some people have the capacity to kill other people, and some people have the capaicty to take an unbearlably painful and time-consuming route to doing it - twas ever thus.