@Packrat That's quite well put, really. I'd sum it up as something like 'they all want to be the lead from Da Vinci's Demons', though I'm not sure how many people have watched it. (It definitely went to those kinds of places, and often aspired to be clever-er-er-er-er-er than that, even.)
That's a good point, though: how do you reasonably place those limits without getting extreme?
How much leeway does someone really have to say: That could feasibly happen IC but we really don't want to take the game in that direction.
I don't think it's necessary to, say, uncreate bats just so people won't make gunpowder from guano (though if someone wants to do that, that's their call and I support their right and choice to make it), or perhaps more accurately, I do not feel it should not be necessary to go that far in order to be able to say: we really don't want to go in that direction with this game/do not want to drastically change the game world in the ways that idea would inevitably change it.
There's some real questions there, I think, and I'm somebody who loves the idea of people being able to add things to a world pretty freely. At what point does the 'little thing' someone wants to add change the game world, or the experience of the game, profoundly enough that it's just not the same game anybody was initially drawn to/initially wanted to play in/would still want to play in?
This is definitely one of the harder 'no's to articulate but it's possibly one of the most necessary ones, not as a control freak trip, but in order to keep the game people signed on to play, well, still the game people signed on to play.