(This is all in good fun. Don’t take it too seriously.)
We don’t need metaphysics.
If we want to know what the fundamental nature of reality is like, we’ll ask the physicists. Contrary to Whitehead, scientists don’t generally need to figure out the metaphysics before they can do the science. On the contrary, they largely dispense with pre-scientific metaphysical notions. Further, if I want an informed debate about what exactly qualifies as causation, I learn a lot more by reading methodological debates among physicists or even political scientists, people who are actually trying to determine what causes what, than by reading philosophy.
Okay, but at least we need epistemology, right?
No, not really. Most of what epistemologists do is try to construct grand systematic theories of epistemology, but we don’t need these theories to learn about the world. Scientists and others all understand that believing stuff on the basis of wishful thinking or without evidence is bad. They don’t need to determine whether process reliabilism or coherentism is the best systemization of our intuitions about epistemology. Further, it’s not obvious that studying epistemology makes you any better at reasoning about evidence.
Okay, but what about logic?
Yeah, it’s fine, but it’s for mathematicians now.
Okay, but what about ethics?
Well, most of what normative ethicists do is try to provide grand systematic theories of ethics, which are of little use on the ground. Just as Einstein’s field equations aren’t particularly useful for studying the path of a falling feather, so Kant’s CI isn’t particularly useful to know what to do in a given situation. Even Kant agreed–he said applying his theory takes “anthropology” and good judgment. Heck, Mill and other utilitarians often worried they’d have to hide their theories from the lay masses, lest the masses mess up the application of the theories.
Okay, but that leaves applied ethics and political philosophy.
Sure, but early on, applied ethics was just clunky “What would Kant say about issue X” -kind of garbage. As for political philosophy, the problem here is that most political philosophers have never studied any economics or political science, and so mostly just do ideologically-motivated intuition-mongering atop a flimsy bedrock of false assumptions about how institutions work. So, at best, this means PPE-type political philosophers who subscribe to APSR might on occasion produce something worth reading.
Okay, but what about aesthetics? Beats me. I have Ph.D. in philosophy and haven’t read a single aesthetics paper.
Should you study philosophy? Probably not. It’s just a time-consuming way of making it highly likely that you’ll be wrong.
Ed. note: Bonus links from Libertarianism.org's Free Thoughts podcast: "What Does It Mean to Think Philosophically?" and "How Much Should Philosophy Influence Public Policy?"