The first criticism is that philosophy can never settle anything because, unlike science, it does not rely on experimental evidence. Granted, philosophers don’t do experiments (other than the very inexpensive thought variety), but then again philosophy isn’t science, so it seems odd to accuse philosophers of not doing what scientists do. (Then again, check out the experimental philosophy web site!)
Philosophers have other ways of settling disputes and advancing their discipline, and these ways make use of the rules of rational discourse and logic. For instance, just like no self-respecting scientist would be caught dead conducting an experiment with a statistically flawed design (say, the lack of a control), so no professional philosopher wants to be found engaging in a logical fallacy. And logical fallacies are even more clearly defined and understood than most experimental protocols.
Moreover, philosophers are not in the business of studying the natural world, so “experiments” in the standard scientific sense would simply be inappropriate. The domain of philosophy ranges over issues concerning the nature of reality (metaphysics), of values (ethics), of knowledge (epistemology), and of art (aesthetics), to name a few. Now, what sort of experiment could possibly be illuminating questions of metaphysics? How would you settle, on scientific grounds, the question of whether there is a real physical world out there, as opposed to all of us being part of the thoughts of a cosmic being, or perhaps simply the holograms of a simulation that someone is playing as a video game? This is not to say that philosophers should ignore scientific findings (e.g., on how human brains make moral decisions), and in fact they do not. But philosophical inquiry has a different enough nature from scientific inquiry that there is no common methodological standard of progress, one cannot be said to be “better” than the other any more than soccer can be said to be better than baseball. They are just different sorts of games.
Now to the second criticism: philosophers cannot be objective or detached from the issues they debate, and besides they have to build their arguments on the basis of one assumption or another, so the exercise amounts to just telling whatever story one prefers. Again, the analysis, I think, misses the mark. There is no question that philosophers are human beings, and as such they tend to seek the same golden trio that most other people (including scientists, by the way) go after: glory, money, and sex, not necessarily in that order.
But philosophical discourse is founded on the same attitude that scientists have of valuing reciprocal criticism and opening one’s arguments to rebuttal and possible refutation. Unlike the case of religion, for instance, philosophers can’t say “I’m right because God told me so,” or “I’m right because it’s written in a book,” regardless of who the author of that book happens to be (that, incidentally, would be a logical fallacy, known as an argument from authority). No, philosophers have to say “I think I am right because...” and carefully fill the blanks with cogent logic, a logic that is mercilessly put under the microscope by their colleagues, because that’s how one gets to publish and obtain tenure (some glory, though usually little money and perfectly ordinary amounts of sex).
As for making assumptions, those can, again, be explored and justified by reason. Besides, scientists have to make a lot of assumptions before proceeding with their work as well, and ironically some of those assumptions are inherently philosophical in nature (like the empirically unverifiable idea that the world is real).
The fact that philosophers continually have to explain and justify themselves, while scientists usually don’t, is a peculiar result of the all-American anti-intellectualism that is so prominent on this side of the pond (in Europe philosophers pack bookstores for readings and discussions, and they regularly appear on or host talk shows -- can you imagine a philosopher on The View? or Regis and Kelly?). Of course, science itself sometimes does not escape anti-intellectual reactions (think of the never ending “controversy” about evolution), but at least science is generally granted the attribute of useful and therefore tolerated as a (rather expensive) academic exercise.
But a society that does not value critical thinking, the laying out of rational arguments, and the use of logic in debating its issues, is a society in decline and risking a return to obscurantism. The irony here is that the most important documents regulating American life, the Constitution and the Bill of Rights, were in fact a direct product of the philosophy of the Enlightenment, and were drafted by people like Thomas Jefferson, with a very keen interest in philosophy and rational discourse. Of course, the Constitution has been under constant assault over the past few decades, in synch with the rising tide of religious fundamentalism and irrationalism. Appreciating what philosophy is about and how it works may make a significant contribution toward reversing that tide.