Never once had a thin or fit person criticize me for it or offer up something unkind, which puts my situation squarely on the opposite end of what you're describing. And I'm pretty loud and open about using this medication class.
Seems to come from two distinct groups of people.
One group judges it and has something negative to say mainly because they can't afford it and have zero interest in cheaper alternative routes, so it's easier to talk trash than admit they'd be using it too if cost weren't a barrier. Since it feels out of reach to them, calling it cheating feels easier than admitting they want it just as badly.
The other group leans toward the idea that any form of dieting or structured exercise is inherently harmful to your body, so naturally a medication that causes weight loss gets lumped into that same category. Body acceptance genuinely matters to me too, a chronic skin condition has left mine pretty scarred up, and I'm choosing to keep living inside it and appreciate it however I can. Part of that appreciation includes working toward getting it to a healthier weight.