I have been wondering lately whether something analogous to Gresham's Law also applies in philosophy: Bad philosophy drives out good (philosophy).
I think the opposite.
Bad philosophy is necessary to define, nourish and refine good philosophy.
Plato, Augustine, Nietzsche - just to name those that readily come to mind - would they have possibly written what they did without their goal to criticize "bad philosophers" ?
It is not uncommon that the only merit of a philopher is that he was so bad as to elicit the response of a better one.
How many of us know of Swedenborg - if any - only because of Kant?
I can hardly conceive philosophy without this initial "taste" for what one likes and dislikes in philosophy.
(And, broadly speaking, criticism and confutation are mainly the attempt to affirm the "good" philosopher's taste over the "bad" 's one).
Then, of course, everybody is free to decide which philosophy is good and which one is bad...