It does make you a bad person. You are body shaming people which is abhorrent - it is the same thing as shaming someone for being too skinny, for being less smart, having small boobs etc. Because of people like you, fat shaming put people constantly on guard about their appearance. Everyone knows that being fat is not healthy but calling them out doesn’t help and it only shows your own bias against fat people. And frankly, calling them fat is none of your business.
And FYI its not poor lifestyle choice always. Lack of diet and exercise are only two of the many factors that influence weight. Genetic predisposition, pregnancy, depression, poor economic conditions and hence buying less healthy food (cuz its cheaper) all contributes to this.