In short: How could you convince a fellow die-hard-formalistic-member-of-the-economics-tribe that the profession has gone wrong because it fell in love with mathematical formalism? And is it true?
One could, or course, give examples. Rational addiction theory, real business cycles, rational expectations, the emphasis on microfoundations in New Keynesian economics. In addition to the problem that the die-hard-formalist will not agree with you on the particulars, there are two problems. First, picking examples do not give the whole picture. Second, it seems difficult to prove that the cause of the problem was an excessive love for formal models. It is certainly easy to get the impression that this is the case when reading these paper, but it is just an impression. I really do not know whether the author/editor was too much in love with formal models. All I can and should do with a paper - formal or not - is to point out what I think is right and wrong in it and perhaps I should just quit speculating about why they were wrong as long as it is impossible to test it more objectively?
Note the "perhaps." It may be possible to link the problems in a paper to its love for formalism, or more generally the problems of a profession, but I think we should dig deeper and not just accept that argument because we agree with it based on our own impressions. We need reasons and arguments that can convince the opposition as well!