Like when you're founding a fascist party as one does from time to time and take over the country you clearly need some group in society everyone can hate to rally around your cause.
If you decide to make fat people the undesirables you can give your cleansing a wholesome twist in that you can release them from the camps instead of doing the stuff where the world gets pissed at you but finally won't do anything about it.
Man I'm on my magical journey to become the most cynical person who ever lived myself but c'mon. There are better reasons to hate someone than their age like for example their weight, fashion choice, how they sound or how much they're into mechanical keyboards.
Man I hope us Europeans are just going through a phase right now. Here in Germany the population didn't take green politics well and global disruptions were blamed on the current government so the far right got an uptick in popularity. Other EU-countries also have the far right on the footstep of ruling and some already fell.