Recently I've talked to someone who said she is worried about those drugs as they will create 2 tier society because only people with money will get thin. This also increases already bad fat phobia in our society according to her.

She has a PhD in biotechnology and works in a lab. She is also quite thin (always was).

It's crab mentality disguised as moral position. It's especially obvious when the same people advocate for free access to drugs, alcohol or gambling. You should have freedom you do anything as long as it doesn't improve your life or move you to in social hierarchy.