[inquest]

It means you probably shouldn't make universal pronouncements about the inapplicability of rationalism to the political sphere

Are we now equating rationalism with reason? If I'm not mistaken, rationalism is a philosophy which demands the predominance of reason in guiding our affairs - which, as you seem to agree (as you've taken it as the premise for your statement above), is self-contradictory. The contrary position is not that reason has no place, but that it has a diminished place. So therefore, I would correct your statement thus:

"It means you probably shouldn't make universal pronouncements about the applicability of reason to the political sphere"

[general_re]

That works as long as you equate rationalism with pure Cartesian philosophy. However, rationalism didn't begin and end with Descartes and Spinoza - consider the rational/empirical synthesis of Kant, where both reason and experience are complementary, and neither is a priori held in primacy over the other. Why shouldn't that brand of rationalism have a prime spot in political theory?