Because you are not elimating the problem just one cause. People will encounter other similiar situations in the future. If someone is not trained emotionally to deal with these events you are harming that person.
Heck, even an adult can't be expected to deal with everything. That's why we have laws against mobbing, harassment and stalking.
Are there any side effects from this training? What if it reduces empathy or causes you become more aggressive. It seems odd if you become immune to constant emotional attacks it would have no other negative effects on your mental well being.
Bullying in adulthood isn't as intense as well in most situations. If someone at work came up to me, pushed me, and told me to kill myself they would be fired.
You might think bullying as an adult involves situations where you get over charged by a plumber or you aren't that aggressive at work so you don't that promotion. I'll admit this does happen but for the most part people who are professional and mature succeed and aggressive behavior is also wrong.