I mean the initial post acknowledges people who have the good genetics to pull it off with the pic on the left. It's more attacking the idea that if a man just lifts he can instantly become attractive (which is an idea thrown around a lot), which is not always the case at all. Some people can lift and it makes no difference, usually because of bad bone structure so they end up looking shit at the end of it.
Presumably if you're on an incel forum you probably have bad bone structure so it's not an out there assumption to make.
If you enjoy lifting for the sake of lifting then no one is going to criticise you, people are just pointing out if you're ugly going to the gym won't make much difference, unless you're extremely fat and that's hiding your good bone structure which can happen, but normal weight ugly dudes who think lifting will suddenly make them attractive are coping hard.