The problem with this stance is that the alternative (making people feel bad) will exacerbate the problem by contributing to feelings of hopelessness and ostracism.
The first prerequisite for making difficult changes is a supportive environment - not a judgmental one.
The problem with your stance is that it is based on a lie, and if pushed enough will break down catastrophically.
> the alternative (making people feel bad)
The actual alternative is to tell the fat people that they really need to fix their serious health problem!
Politely watching them die before you is maybe comfortable, but pretty messed up.
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.