I watched Looper again recently and something was bugging me. If the future can control where the victim will go, why not send them into something that would destroy their body? Like into kiln or something that would cremate their body and destroy all the evidence? They obviously know where the body is going to go, since the looper is there to kill them. Why not kill them and dispose of the body at the same time?
This was explained in a series of interviews with the film's director; Rian Johnson:
"But I also thought of doing a scene where he (Daniels) says that he’s been complaining to his bosses that this is a stupid system and that they need to find another way. But at the end of the day, it didn’t end up making the cut. The one other thing, and we actually had a line that we cut out in the diner scene, is the fact that the time travel device is not adjustable. That fact that it is set to an exact time and you can’t change when or where it sends you back to. And maybe I should have left that piece of information in the diner scene. But it was part of this longer discussion that Bruce and Joe had that we ended up snipping out to get to the heart of that scene.”
Since the location + time are fixed, they can't simply beam them into space, nor can they zap them into the dim and distant past
“People in the future, all they know about time travel is to be afraid of it. So they’re trying to keep it as tight as possible. So the initial reason they set it up this way was to keep the causality loop as tight as possible,” Johnson said. Because, for example, if someone else kills your older self and you have to exist with your own murderer for 30 years, what’s stopping you for murdering them or doing something to screw everything else up? ”Every bit of evidence is gone from that loop when you kill yourself,” he said.
The short answer is that their plan ensures that the victim is actually dead and creates a closed temporal loop. Any automated method doesn't account for any accidents nor the fact that no automatic execution method is completely foolproof.