Why do people hate fat people?

Because they are a social disgrace for not taking care of their bodies

Answer:

People do not generally hate "fat" people. Prejudice against any group an occur based on ethnicity, national origin, appearance, religion or other criteria can occur. Even "beautiful" people, ambitius or well educated people (these are often seen as positive attributes) complain that they are cut out of job interviews because they might not be willing to be long term employees.