I don't think he's saying it's supposed to help the people being laughed at - it's supposed to help the reader, by de-normalizing and shaming fatness, so they are motivated to become or stay thin. The target is collateral damage.

I don't really buy it, it's transparently a post-hoc rationalization for a sub engaging in the age-old business of being nasty to low status people because it makes us feel good and superior.

You can click on "view the rest on the comments" on that voat thread he linked to to see what's it's really all about.