Quote Originally Posted by Alfred Pennyworth
Because he thought it was good sport. Because some men aren't looking for anything logical, like money. They can't be bought, bullied, reasoned or negotiated with. Some men just want to watch the world burn.
Unfortunately this is very true about the world we live in today. Some men just want to watch the world around them burn, there is no rhyme or reason to how or why they kill, not for the true sociopath at least.

The fact that Gacy, chose to commit his murders I think indicates rather to the fact that when he was killing he was doing it with a reason and intent. He wasn't doing it because he enjoyed it, rather he did it out of desire to continue his specific way of life.