Even if the Middle Ages were no worse than quaint (and they were much worse, immeasurably worse than quaint), the ideas current then have to be called obsolete today.
That's certainly true of some ideas, not true of others - for example, the characteristically modern emphasis on reason and logic, or for that matter what historian of science Lynn White called "the invention of invention", were medieval phenomena that never became obsolete. Not to mention a great many philosophical, juridical, and other notions. Other ideas didn't become obsolete so much as get built upon, even though the "state of the art" has advanced considerably in so many areas.
If Randi uses “medieval” to describe modern attempts to promote exploded modes of thinking, that’s an acceptable kind of rhetoric. He objects to those who would slip backward and downward into magical, irrational thinking.
Yes, but why repetitively associate that specifically with the Middle Ages - an era that laid the foundations of modern science and during which (as Prof. Grant persuasively argues) the Age of Reason was born? Doesn't that obscure the fact that it was during the Renaissance (the post-medieval one, not the 12th-Century Renaissance) that - in historian Jean Harris' words - "magic, divination, astrology, and other forms of what moderns dismiss as occultism experienced a notable revival in Europe, shaping both elite and popular culture"?