What you're arguing is a philosophy called teleology. Essentially, it's a philosophy that things exist for a "final purpose".
For one, it's not a Christian concept — it's Aristotle, and it's only used in our circles because Middle Ages theologians had a huge hardon for Aristotle.
For two, while it was used in Aristotlean ethics as a tool to focus problem-solving methods, deductive reasoning, and study of nature, it did not originally have moral
connotations. Even if one accepts the premise that things have an immutable final purpose, it's kind of a non sequitur to say any other use of that thing is morally wrong. By that logic, it's a sin to use my chair as a footstool while changing a lightbulb.
Amusingly, our use of teleology to dictate our moral constructs is a violation of teleology's teleology.
To extend that, if I were to take a coworker's programming code and extend it to do something it wasn't designed for, we don't call that a moral failing — we call it robust and flexible design, and it's a good thing that we encourage at every turn. Similarly, it seems rather arbitrary to pick a function of the human body and say "this was designed for X, so it's wrong to use it for anything that's not X". To the contrary, I'd say its ability to do Y and Z as well is generally a good thing.
edited 19th Oct '13 1:36:40 AM by Pykrete