I'm staying away from the fat thread. I almost wrote a tl;dr
As a fat guy I can say anyone who thinks being fat is, or can be, as healthy as not being fat is delusional. Over the history of billions of people being on this planet have there probably been some fat people that have had good health with no major problems for the majority of their life, probably, but lots of weird shit happens and it's not normal.
Dude's whole argument is skinny people can be not healthy too, no shit. That's not the point though.