Caplan isn't some interloper with no knowledge of any of the material he touches on ranting on Twitter. The man has a career as an economics researcher specializing in public-sector work and actually teaches economics at a reasonably prestigious university (I have heard of George Mason). Perhaps we might pause to consider that he may be, in the realm of his specialty, not a complete fool. In general, his work would seem to be worth engaging with by his peers.
With that in mind, it is a little concerning that so many people are so ready and willing to argue with his claims yet none are interested in engaging with his work or methodology. Perhaps they, as you, are dismissive because he reaches conclusions they find so implausible as to be not worth engaging with. Or perhaps because as he alleges, the field simply does not value quantitative argument beyond its ability to get a paper published.
For my own part, I think it would be educational to know which is the case. If the former, I would like to understand if this is politically motivated (and a lot of things are in economics, especially in a policy context). In the latter, it leads me to question just about every claim from the entire field, including Caplan's.
I'm not equipped to evaluate his data or critique his work. I won't make the attempt. I would hope for better of his peers, though.