This is a really interesting piece from The Guardian discussing society and its acceptance of fat people.
Weight has been pathologised in the same way. Phrenology was a respectable movement even though it was based on a phoney notion. It, too, had an ideological bent. The bumps on the heads of those of European extraction were supposed to prove that they had superior skills.
The article takes a look at different angles of fat acceptance, but it concludes by pointing out the fact that judging someone based on their weight is still prejudice. Whether or not you believe someone can change their weight (an idea I have dispelled), the mutability of a condition of prejudice doesn’t excuse prejudging someone based on that condition.