Jan Velterop has published "Are 'Predatory' Journals Completely Negative, or Also a Sign of Something Positive?" in SciELO in Perspective.
Here's an excerpt:
Yet, even with the drawback of being polluted by predatory journals, a functioning market is preferable to a quasi-market, completely dominated by monopolies or monopoly-like players. A system of subscriptions, in which the party who pays—the institutional library—has practically no meaningful choice of what to buy, differs from one of article processing charges (APCs, which make open access possible), in that the party who pays—the author—is the party who does have a meaningful choice of where to submit and publish. So 'flipping' the system from subscriptions to APCs does deliver something much more akin to a functioning market, and 'caveat emptor', 'buyer beware', applies to all markets.