I would neither like when my son were to participate in such a competition as a slapper nor would I like if he was standing around screaming like a cheerleader when his favorite slapper humiliates his opponent. That is just stupid. I don't like boxing either because I think that our brain is so valuable, it allows us to do so many things, feel so many things and so on. Why get it slapped permanently until it might take damage and stop working accurately or maybe even lead to death? That is just not my thing I guess.
Every professional sport causes serious injuries to athletes. Soccer players often have problems with their knees and feet, jumpers have problems with their spine, boxers have problems with their head.
To avoid serious injuries, you can practice boxing for 2-3 years. After that, you can just keep in shape. Such training makes a person very tough and strong in spirit.
But there isn't most likely even a decent ratio in slapping tournaments in terms of risk and reward. When you trash your knee as a professional soccer player for 20 million EUR in your career, well fine, and you usually don't have any problems with your brain. The goal is to score goals, not to trash someone else's face with a single hit for a couple of bucks, risking the other person's health. But I might just be different though. You know these fail videos where people break their bones in gymnastics and so on? I can't watch them, but I know a good number of people who can laugh about it, I just can't. ;P
To become a professional footballer you need to dedicate your whole life to soccer and it's not a fact that you can earn 20 million euros and not play for some obscure club. I think people participate in slap competitions because of the hype and gaining fame that can eventually provide a good income.