Force would mean throwing them in fatty prison or something ridiculous. People can do what they want, I'm still going to encourage them to get healthy. I have yet to talk to someone who regretted getting their weight under control, even those who used to claim they were fine with being overweight. Think of it like just encouraging exercise independent of weight (which is also good for you, regardless of mass status). I'm not going to force anyone into a lap pool, but I will tell them about how good exercise is for you.