Brotha waattttt?

If your genetics give you an abnormally slow metabolism, this will result in you gaining weight based off calories that a normal person would eat to maintain a healthy weight. It's hard enough for most people with normal metabolisms to eat a healthy diet so saying "well those people can just control it with diet" is grossly optimistic and again puts the "blame" on these people with metabolic disorders for not eating well enough.

You did mention though that those people may go the pharmaceutical route, however that may not be available to a lot of people due to lack of health insurance, lack of knowledge, etc.

So to come full circle, yes, some people are fat because of genetics.

To be fair, this is a very small subset of people we're talking about.