You misunderstand, or I didn’t explain it well, because you’re making the same argument that the constitutional scholar is making against originalists.

By narrowly interpreting the text exactly as a WL18CWM would have interpreted it (e.g. black people are not people), they’re not leaving room for interpretations of the constitution that would provide equal rights to people who are not WL18CWM:

  - The constitution grants rights
  - The authors have a bias (WL18CWM)
  - Originalists essentially ignore this bias, leading to fewer or restricted rights to people who are less similar to WL18CWM

>If a person is incapable of reasoning outside of their class/race/gender/etc position, then how is a fair law even possible?

An entirely fair law might not be possible, at least as long as people with specific class/race/gender interests overwhelmingly influence it. But a somewhat fair law or a law fairer than another, is.

And, at least as I understand it, the scholar doesn't say that nobody is ever "capable of reasoning outside of their class/race/gender/etc position" in general. Just that those making the constitution weren't that good at it.

A reasonable initial place to draw the line might be "owns slaves".