I have suspected for a long time that DM wanted to establish a murder for hire and/or body disposal business. There would be big money in this, and he thought he needed a lot more money coming in each month. Such a business sounds like something out of a crime novel. I think all the power and excitement greatly appealed to him as well. He got rid of people that got in his way, like his father, then Laura. Her death may have been in part because he wanted to test the Elininator. It was easy, so he planned to kill the owner of a truck, and steal the truck. If he and Smitch had not been arrested, and put away for life, they likely would have killed hundreds more people, or at least helped other criminals dispose of bodies for a big fee. That eliminator was on a trailer, and the man who sold them said no one in his company had ever seen one mounted that way to make it easy to move around. They might have traveled to other places to kill and/or dispose of bodies, not always using the hangar. IMO
I've always thought that too - that he probably intended to disappear murder victims as a service for large sums of money.