Morkus from Orkus
It is not railroading to insist that a player adheres to the accepted themes of a world. It is poor form for a player to try to ride roughshod over said themes however. A DM has the right to veto anything, a good DM will use the veto sparingly, and a good player would ensure the DM never needs to use this veto.
Yes it is. If you are forcing the players to go down the rails you provide(the game does not make it impossible for druids to put on metal armor), then you are in fact railroading that player.
My comments about Cthulhu was pertaining to Middle Earth, not D&D, I am aware of the existence of both S3 and WG4. If a player tries to play a Cthulhu cultist in Middle Earth, then refer to my point above.
And the point goes flying over your head. D&D has precedent for allowing things in that "break the rules," so forbidding exceptions goes against that tradition.
I am curious, though. Are your paladins human only? Do female characters cap out at 17 strength? Can demihumans not go to max level? Those are all traditions every bit as old school and strong as the druid one.
RAI is clear to me - a Druid will not even attempt to wear metal, it is against his or her ethos. If a player cannot accept that they they won't be playing a Druid. The player should not even try to push this.
Your rails are squeaking. Maybe you shouldn't have made them out of metal.