I've seen a lot of ex-vegans on Reddit argue against veganism and a lot of the time they resort to things like lions tho or plants feel pain.
I think if they tried it and it didn't work for their GI tract and then they switched back, they'd be more like "I wish I could go vegan but I can't". I don't get how you could understand the moral arguments enough to actually go vegan and then go back on them like that, so I'm thinking most ex-vegans never really cared in the first place and were doing it for health reasons/were just plant based and misunderstand the labels.
Either that or the carnivore types never actually tried and just want to say they did to strengthen their argument.