Quote Originally Posted by NichG View Post
Putting an explicit mechanical penalty on something like that makes it a subject of optimization - that is, the druid in character would always want metal armor if they could get away with it, but because there's a cost they may decide to pay the cost to have metal armor, or avoid the cost by avoiding the armor. That establishes a different kind of world than one where 'druids have a mentality that rejects the use of metal armor as a desirable thing'. In the former, druids are mercenaries who only do the things they do in order to trick nature into giving them powers, while in the latter they're true believers in some ideological elements and, as part of their practice, learn to gain powers.
Firstly, adding a mechanical penalty doesn't automatically make a druid just hold nature hostage for powers. You may play a character that way, but that doesn't define literally all dnd druids to exist as nature-thieves, that's just a real stretch.

Second, cool? If you don't like that way of thinking, then don't go with that. I also said you can just not have a restriction (it's a stupid one in the first place but whatever), what about that?