- Maybe there's no such thing as an "expert" in philosophy. Philosophers specialize in sitting and thinking. We can all do that! Sure, philosophers do it more than non-philosophers, but that doesn't make their conclusions more likely to be correct than ours.
Sure, maybe there is no specific methodology unique to philosophers. Perhaps it's something we can all do. So Caplan could become an expert on this issue if he devoted the time to it. It's just that he hasn't yet. That's relevant.
- Perhaps we can ignore so-called "experts" in philosophy. Philosophers of ethics are just really, really sucky when it comes to figuring out the answers It may just be that their methodology sucks. Sitting and thinking doesn't get them closer to the right answer at all.
(By the way, this point, along with most of the argument in these past few posts, comes from Bryan Frances.)
To avoid this, you'd have to make the case that expertise in philosophy, unlike expertise in other disciplines, actually worsens your epistemic position.