My personal experience was that the shame I'd been made to feel throughout middle school for being overweight fueled the motivation to buckle down and lose weight when I was independent and mature enough to come up with a diet that I could sustain.

Glad to hear you came out alright.

I’ll offer this argument: Society aggressively tells overweight people that it is bad to be overweight, in no uncertain terms, and with significant repercussions. Yet overweight people exist. Hence, the strategy of shaming people until they lose weight does not work in the general or average case.