Having been sober for nearly 20 years, I can say that when I quit drinking and using, It was not beneficial for me to fantasize about getting loaded. Better to think about something positive in life and try to help someone. I'm not sure that in this case mental health experts really know what they're talking about. It is also entirely possible that I don't know what I'm talking about though. My experience is with obsession over using mind altering substances, not killing people. But still, I'm not sure one obsession would be better controlled by one action, which actually encourages another type of obsession. Hard to say!