This is a terribly naive view of philosophy. The author is teaching analytic philosophy, while postmodernism (no need to bring in deconstruction, which is entir

This is a terribly naive view of philosophy. The author is teaching analytic philosophy, while postmodernism (no need to bring in deconstruction, which is entirely irrelevant to your point) is continental. Analytic philosophy rejected postmodernism for reasons similar to your argument, though postmodernists were not so shortsighted as to not anticipate your objection and address it. No, anything does not go in philosophy. Philosophers become prominent precisely because of the persuasiveness, clarity and and resilience of their arguments, much like science. Science, after all, was birthed from philosophy, and the most active area of contemporary analytic philosophy is philosophy of science.