This is really a matter of what YOU think, but here's an idea:
If we think that in general it's a good idea to conserve natural resources so that they don't get used up, then part of the responsibility for making that happen is on our shoulders.
Think of it this way: the stuff we use is made by companies. Companies will make more of the stuff we use, and less of the stuff we choose not to use. So if we want certain materials to be used more or less by the companies making our stuff, our buying patterns should reflect that.
Where the ethical question comes in is WHY we would want to conserve. Maybe it's because we want to make sure that there are enough resources for future generations. Maybe it's so that areas where these resources come from aren't permanently depleted, leading to loss of habitat for wildlife and the loss of livelihood and a livable environment for locals. There are all kinds of ethical angles to be considered, but the lingering question would be, "If it's not our problem as consumers, whose problem is it?"
Hope this helps a bit.
Matt in NY