This has been my sticking point, as its ridiculously childlike in its viewpoint. Really? So under no circumstance would a druid wear metal armor? What about to prevent the end of all creation. Tharizdun is going to destroy the world unless Treehugger Pete wears this helmet for a minute... well, it was a good run.
Moreover, this is in fact, the only listed "sin" for druidism that is treated in terms of absolutes. You can choose to burn down your sacred grove and open up a toxic waste dump in the spot, but your devotion to not wearing metal is such that you cannot even choose to violate that tenant of your religion. You'd think that level of blind dogmatism would be reserved for the lawful faiths. Its just absurdly simplistic. Some kind of penalty, but still allowing the character the choice, would have been better (particularly given how they suffer no other metal related restrictions).
Though I kind of want to run a game similar to the A-Team, where they have to druid the druid, knock him out, or hypnotize him to get into the Apparatus of Kwalish. "I ain't gettin' in no metal, fool!"