It is hard to say exactly what doing philosophy achieves. It is certainly not the case that any philosophical question has ever been definitively answered, or even given a best answer (a best answer being one that is universally accepted as perhaps not fully correct but better than any other answer so far proposed). If you think that it does then you must not be paying much attention to philosophy as a whole. There is no theory, however well refuted, that is not on occasion revived by a philosopher in some new form. For example, recently I have seen idealism proposed as the best theory about the world in light of certain problems. If we can’t produce philosophical theories that are definitively better than idealism then clearly we haven’t produced a definitive answer or even a best answer to any problem, because having such answers would make the revival of old philosophical theories unthinkable.
But, on the other hand, we needn’t suppose that philosophy is so like science that there is always a best answer to a given problem. Maybe philosophy will one day produce such answers, but in the meantime perhaps we are just making progress towards such answers, possibly by ruling out bad theories. I would like this to be true, but I can’t honestly claim that it is the case. I admit that some philosophical theories are on occasion refuted, for example by being shown to be internally inconsistent, but I have a hard time seeing this as progress towards a solution because it is never possible to eliminate all the possible variations of a theory (at least the way we currently do philosophy), and since there are an uncountable number of ways to alter a theory being able to rule out a specific variation of a theory isn’t really progress in any significant sense (as the example of idealism being taken up again shows).
Now before I get to my point (no, I’m not there yet) I should reply to an objection some might raise against what I have said, namely that it presupposes that philosophy should be aiming for true philosophical theories. There is no need to respond to this objection directly, it is sufficient to point out that current practice of philosophy also presupposes that it is aiming for true theories; the fact that we take internal contradiction or contradiction with certain established or intuitive truths to be reason to reject a philosophical position is evidence that we are searching for true theories. If we weren’t searching for true theories contradiction wouldn’t be a problem and hence wouldn’t be reason to discard a theory. Of course there could be something wrong with the way we currently do philosophy, but that is one of the claims that I am trying to motivate with writings such as this one. So to say that philosophy isn’t a search for truth is to concede my point, but to draw a different conclusion from it.
In any case a better response and, more importantly, one that is actually made by some philosophers, is that what philosophy currently produces is a better understanding of philosophical problems. (I suppose with the idea in mind that when we achieve a certain level of understanding then we will be able to give them definitive solutions, and that we haven’t been able to give them such solutions yet because our understanding of them is currently insufficient.) This is a possibility that sounds attractive, but ultimately the way philosophy currently proceeds implies that a better understanding of the problems, even if it really is something that we achieve by doing philosophy, is not something that we can point to as an accomplishment of philosophy. The difficulty here is that if a better understanding of the problem really is usefully and really will bring us closer to providing definitive solutions in the future then why aren’t philosophers attempting to share that understanding? Philosophy is done and taught through attempted solutions to philosophical problems. Which means every philosopher has to develop an understanding of philosophical problems on their own. This doesn’t rule out the possibility that we understand philosophical problems better than the philosophers who came before us; possibly reading modern philosophical papers gives leads to a better understanding of the problems than reading older papers does (although if that is the case why do we even bother teaching students anything besides modern philosophy?). However if a better understanding of the problems is important and actually a step towards solving those problems then why isn’t that understanding conveyed directly? Certainly it is possible to write papers and books which direct all their attention on understanding the problems and, more importantly, to teach such an understanding by itself. But we don’t do philosophy that way, we continue to produce papers and books which purport to solve particular problems or refute the proposed solutions of others. And we continue to teach philosophy by exposing students to what are thought of as the most important attempted solutions, which clearly seems like an effort to teach them to be able to create novel solutions of their own, not to lead them to a better understanding of the problems. Of course this doesn’t refute the idea that a better understanding of the problems of philosophy is what we should be after, but it does show that the philosophers who make this claim don’t really believe it (this doesn’t make them hypocrites, it could be an unconscious disconnect, possibly a result of cognitive dissonance), otherwise they would do philosophy differently.
Now I won’t deny that philosophy has a number of side effects. Doing philosophy can make you a better reasoner and can improve your rhetorical skills. Philosophy can also serve as an inspiration for social improvements (example: natural rights). But these are side effects and not something that we can count as an accomplishment, because we could do better at them by studying them directly, without doing philosophy at all (although thinking about how society could be improved might be considered philosophy by some I think if a practical focus is maintained it can be subsumed into sociology or anthropology). So then what does doing philosophy accomplish? Not much I would say. I think it does lead to plenty of great ideas, some of which might be close to definitive solutions to philosophical problems. But I think philosophy as it is currently pursued prevents us from ever accomplishing anything that will be later looked back on as progress towards a solution. (Certainly the history of philosophy will still be studied, but as with the history of philosophy today it is never clear that the historical development of philosophy embodies progress; past philosophers certainly had interesting ideas, but it is a stretch to look back on them and see them as getting closer to the truth, as they tend to wander all over the map with no clear direction.) This then should motivate some kind of change. Obviously nothing I have said here says what that change should be, both giving up the idea of philosophy as leading towards truth and changing the way we do philosophy to focus on understanding the problems are possible ways of solving the problem I have raised here.