Is it wrong to always judge fat people?
Why do you judge fat people?
Because they make me sick.  When I see them eating food, I can't eat as a result.
Being overweight can be unhealthy, and some people are irresponsible with their eating, but it is much worse to judge people based on their weight.  The fact that you were fortunate enough to be thinner than them does not make you superior.
You don't know anything about me, don't discuss my food or the way I eat with me.
We are talking about your disgust for overweight people here. Sometimes it's genetics, sometimes laziness; still, show some empathy and don't judge their situation so harshly.