It's like if someone referred you to Boyle's Law and you insisted someone from the 17th century couldn't possibly have anything useful to say about physics.

By this logic, one could also argue in favor of Newton's theories on alchemy because he essentially invented classical mechanics.

Consequentialism is a type of formalization of ideas on ethics, which are inherently arbitrary. Theories of political structure deal with empirical matters of actual results. taw asserts that someone in the 17th century would have had no empirical data relevant to modern govenment, an assertion that is, if not obviously correct, at least defensible to the extent that society has changed since then.