There's a gazillion twin studies out there. There are huge databases of twins to facilitate their creation. It's really not that difficult. They might be imperfect but I would not call them unreliable.

We already know from earlier twin studies that genetics play a large role in literacy and numeracy.[0][1] So it's not like this is a shot in the dark, everyone already knows it's a confounder that must be taken into account.

[0] https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7610.... [1] http://journals.sagepub.com/doi/abs/10.1177/0956797613486982

I give the post credit in that it provoked your comment and some potentially enlightening discussion for someone not entirely familiar with the study of human behavior (like me). For instance, I would have thought that twin studies might be considered reliable for purposes of accounting for genetic confounds with respect to aspects of human behavior. It sounds from your comment that they are not.

On the OP getting warned, it wasn't immediately clear to me if the objection was more about a) knowledge that Matthew Yglesias didn't read the study and therefore was not in a position to summarize his analysis with a pithy analogy and be quoted, b) the use of any pithy analogy itself, or c) the use of an analogy that seemed to explain a confounding issue? There seemed to be some additional, non-obvious context missing (at least to me) that led to the warning.