Too many parachutists are wayward, ill-disciplined yahoos. Add to that the nervous bravado displayed by many, in order to appear macho before a jump (especially if there are girls around) and you have a recipe for disaster. I can just imagine them larking around in the back of the aircraft; the unfortunate pilot had no control over them and he will be castigated at the enquiry. They should all be strapped in, like any other passengers, until they are at a safe altitude.
One of my mates (JB) was dropping parachutists from a C182. The PJI was the last one out, and, for a joke, leaned over, withdrew the ignition key and took it with him. JB was now faced with a real forced landing, which he carried out immaculately.
JB beat the PJI to the ground, secured the aircraft and then beat the PJI to the ground!