LogFAQs > #979572072

fat people are one of the most socially acceptable groups to be openly repugnant toward, because a common belief among people is that bullying works when it comes to obesity.

That said I don't think the OP video is showing a common attitude. Way more often people are happy seeing a fat person work out because it validates how they broadly treat and view fat people. That fat people hold immoral qualities like sloth and gluttony, so they deserve abuse not just to help them stop being fat, but because fatness is a visible indicator of inferior spirit. So when a fat person is seen trying to lose weight, it's viewed as an acknowledgment that they're bad as they are, rather than simply a health benefit. (Obviously there's also plenty of people that are just happy a person may feel empowered to go to the gym and are getting healthier.)

Over time though it is going to become much more widely understood that obesity is a disease especially as treatments improve.