Another hazy issue. I think if your going to keep fish, try and keep them in as realistic an environment as possible. Now I myself prefer the look of real rock and driftwood. But to be honest your fish will hide in a plastic made cave as readily as they will a cave you've painstakingly created by hand from real rock. They don't give a sh*t really, they just want a place to hide out. Now I can appreciate what catfishmike is saying. If restraint was everyone's rule of thumb, we'd have a lot less problems. Sure, go ahead and pick up some rock for your tank. You don't have to get it from a river, a nice rock from the middle of a field works just as well. Just be careful and show restraint. But we can't go to off the deep end on the environmentalist kick. All the arguements about hurting the environment to procure this rock and wood your putting in the tank also applies to the fish you already have in your tank. Their snatched up out of the water because of the price they fetch, and this can upset the balance as well.
So, if you already have fish in a tank, which whether you want to admit or not, ties you indirectly to some shady fish practice somewhere, then you might as well make a nice environment for them, because to argue environmental issues over the "furniture" in your tank, and not also on the fish at the same time is a little hypocritical. I don't like poor and damaging practices of fish and/or aquarium "furniture" procurement. But I like keeping fish, and I like making a natural looking environment for them. So I am indeed a bit of a hypocrit...but I'm ok with that, how about the rest of you?