Nothing Has A Purpose
The first objection is that it is rubbish to talk about natural purposes, because we merely imagine them; the purposes of things aren’t natural; they are merely in the eye of the beholder. But is this true? Take the lungs, for example. When we say that their purpose is to oxygenate the blood, are we just making that up? Of course not. The purpose of oxygenation isn’t in the eye of the beholder; it’s in the design of the lungs themselves. There is no reason for us to have lungs apart from it.
Suppose a young man is more interested in using his lungs to get high by sniffing glue. What would you think of me if I said, “That’s interesting—I guess the purpose of my lungs is to oxygenate my blood, but the purpose of his lungs is to get high”? You’d think me a fool, and rightly so. The purpose of the lungs is built into the design of the lungs. He doesn’t change that purpose by sniffing glue; he only violates it. ...
Consider the young glue-sniffer again. How should we advise him? Is the purpose of his lungs irrelevant? Should we say to him, “Sniff all you want, because an is does not imply an ought”? Of course not; we should advise him to kick the habit. We ought to respect our design. Nothing in us should be used in a way that flouts its inbuilt purposes.
This does nothing at all to support the contention that there are real purposes to things. I maintain that the idea of inherent purpose is, in fact, rubbish -- all there are are different uses that someone may make of a thing. Some of these uses may be ineffective -- your lungs will probably not make a very good paperweight. Others may be effective at producing bad results. The glue sniffer, for example, will pretty effectively produce a variety of health problems and ultimately an early death, which are bad because we can safely assume he doesn't want them.
How a thing came to be can be useful input into judging whether a use will be effective and what results it will produce. But it's not morally determinative. What's morally determinative is our evaluation of the results. Re-purposing a thing to new uses is a valuable expression of human creativity, not a form of poor discipline to be met with raps on the knuckles.
Ultimately, "purpopse" arguments depend crucially on the implicit assumption of design -- that a thing's existence is due to the intent of an obedience-worthy being. (Thus calling this type of philosophy "natural law" is false -- it's actually "divine law," since it's divine intent rather than the resulting structure of nature that matters.) Why God's intentions should matter to us (matter inherently, that is, since divine law arguments aspire to more than "do it or you'll get sent to hell") is unclear, except that it's a useful cop-out.
I mentioned above that there's a clear way to judge uses -- by their consequences (I tend toward "satisfaction of the desires of all affected" as my metric of consequences, but the exact metric is not relevant here). Buziszewski seems unable to comprehend such a thing, imagining that if "(the designer's) purpose" is removed from the equation, there's no way to tell if what you're doing is good or bad. This is the morality of the fatalist, the paper-pusher at the bottom of the hierarchy who is either too sycophantic or too soul-deadened to exercise any judgment, who takes refuge in "just following orders," who wants nothing more than to be a cog in someone else's machine.
The other day, I got an email back from tech support in response to reporting a minor glitch in a program. The tech support guy's message was petulant -- he essentially told me that I wasn't supposed to be using his program the way I was, because I was exploiting an unintended loophole, and therefore he had no sympathy for me in encountering that glitch. Buziszewski would probably have been chastened and dutifully begun using the program only in the way its authors intended, since that's its purpose as revealed by the designer. I, on the other hand, weighed the consequences -- the annoyance of having to work around the glitch to use the program my way versus the annoyance of the extra steps involved in using it in its intended fashion -- and decided that continuing to use it my way had the best overall consequences in terms of my time and the value of the files I was producing.