Positive reinforcement is a psychological tool. Negative Reinforcement is noted to not work as well on dogs, and it doesn't work at ALL on Cats, supposedly. Instead, you need to have them do something, then give them a treat. Eventually they learn that 'sit' means to sit down on haunches, and that it is good, because they get a treat, usually.
(DISCLAIMER, I ONLY TOOK A SINGLE COLLEGE PSYCHOLOGY CLASS)
I believe Positive Reinforcement is the preferred method, but it is harder to make sure it is well earned. Look at honor, people just forget to give them out, so you don't get it. And Hextech is still technically negative reinforcement. You lose something for being toxic.
If honor actually was used reasonably, it would be a good incentive to be positive. But it's hard to make honor be used properly. I believe they are still hunting for a positive reinforcement tool, though.