And so, with one unretracted tweet, Welch has effectively rendered himself irrelevant in the so-called thought-leadership world he has dominated for so long. It’s fine to have unusual or minority opinions. What’s not fine is to base those opinions on nothing but ideology, and admit of nothing which could make you change your mind. At that point, you’re not a thinker any more; you’re a theologian. Welch has clearly decided that he would much rather be a pastor, preaching to a like-minded flock of WSJ op-ed page dogmatists, than a participant in substantive debate. The sad thing is that he received much more attention for his outbreak of crazy than he received in response to any of his less-bonkers pronouncements. Which is probably only going to encourage him, going forwards.

Felix Salmon is an Audit contributor. He's also the finance blogger for Reuters; this post can also be found at Reuters.com.