I was reading a post by Will Wilkinson in which he quotes Brad Delong quoting Keynes (it's complicated) thusly:
Let us clear from the ground the metaphysical or general principles upon which, from time to time, laissez-faire has been founded. It is not true that individuals possess a prescriptive ‘natural liberty’ in their economic activities. There is no ‘compact’ conferring perpetual rights on those who Have or on those who Acquire.This fascinated me because Keynes clearly felt that a philosophical argument was needed in order to make progress against those he felt were failing in their stewardship of society (by putting individual interests above those of society). The belief in natural rights is definitely a philosophical belief (and often a religious one as well) and it's hard to really regulate and manage an economy if you have natural rights standing in the way. As a quick example, if someone has the right to dispose of their property in any way they choose (which would be linked to the natural right to property which John Locke proposed), under what right could you regulate how someone disposes of their property, either by taxing them or limiting their freedom to trade that property with others? The point of natural rights is that they are inalienable, and no one (not even the rights holder) has the power to give the right up.
I don't personally believe in natural rights. It's hard to imagine where they might come from. John Locke, for instance, believes we get them from God, hence the bit in our Declaration of Independence "[all men] are endowed by their Creator with certain inalienable Rights...", but I don't believe in a supernature that could give us those rights, and I can't see how they'd come from the natural world. But it's not the issue of natural rights I find fascinating here. What I find fascinating is that Keynes felt he had to make a metaphysical claim in order to support his economic ones. Granted, he made a very poor philosophical argument (it's generally not a good idea to just assume what you want to prove), but he still felt he had to address the issue. Why?
I think it's because in the end, our studies and endeavors aren't as segregated as we'd like to believe. Economics can't exist in a vacuum without relation to science or psychology or social studies. All human endeavors have humans as their common denominator. I think I'm getting closer to finding out where the reason for philosophy comes from, and I think it has to do with this idea of interconnected fields of study. In the post about education, I talked about how science relies on an epistemological claim that we can know things about the outside world. To justify political science claims, you need to deal with notions of morality and rights. Keynes needed to rebut a philosophy in order to make room for his implicit one (that societies have a right to protect their interests, even against the interests of individual members of that society). Whether you want to deal with it explicitly or just assume it implicitly, claims about reality rely on a philosophical groundwork that supports your ability to make that claim. Everything leads back towards philosophy.