You hit it right on the head bonnie; Scott was a true socialpath, as testified by his peers this morning on Good Morning America. They'd testified that he was quiet all the times and didn't want attention; these are early signs of some form of psychosis. Such people tend to develop their "own world" in which they can do whatever they want.
I wouldn't be surprised if in Scott's "sick world", he felt that Laci and the kid was a bad choice, and that he'd felt he had the power to erase them; so why not kill them and start from scratch, with a new woman and a new place?
I once had to kill a dog because he'd contracted rabies. My kids asked me why I'd done it. I'd answered, "Because this animal is too sick to remain amongst us. It was time to put this sick dog to sleep."
Scott is a sick dog; I'm not surprised that the jury put that sick dog to sleep.