This varies with personality and situation - I know exactly what you mean because I was shouted at for being fat and lazy as a child and it never did any good, but I can also think of many situations in my own life where the opposite was true and people yelling at me for failing provided the impetus to do better...
I think the risk of not doing anything is worse though. If poor behaviour is tolerated, and not given some kind of negative feedback then it can become accepted. I suspect this is part of the obesity problem - if living as a fat person were really horrible less people would be inclined to do it and, at the risk of sounding cruel, if medical help were refused for obesity related problems then the genetic element would take care of itself...
I'm fat - and if I die because my heart clogs up with all the byproducts of that fatness then it is my own /stupid/ fault.