The trick, as the study says, is to use therapeutic doses of negativity to avoid an overdose that would result in the opposite of what you intended to happen.
You don’t want to crush them.
Well, yes, that's the problem.
If you're indiscriminately spreading anti-fatness propaganda everywhere you go, you'll probably shame a couple fat people into getting on a diet, but you'll probably also aggravate a couple of your viewers' annorexia.
There are other problems with fat shaming as well, such as the disproportionate effect it has on women (fucking beauty standards) and the unhealthy effects of crash diets. This sort of thing needs to be handled slowly, and with a doctor monitoring it, not something that a desperate victim of bullying is going to do. Losing a lot of weight, and then gaining it back, is really bad for you, and “if fat shaming isn't working, do more of it” is not going to cut it.