One of the instructors in my graduate design seminar related a reaction that someone once had during a class exercise years ago. It went something like this: "Why should my work serve future generations? What have they ever done for me?" He brought it up as an example of the egocentrism he wishes designers to purge from their mindsets. But I think a serious consideration of these questions reveals a very compelling answer in favor of a future-oriented approach in design.
What have future generations done for us? Well, their very existence validates that the present generation will have survived successfully enough to propagate our species. We won't have blown ourselves into oblivion or rendered our environment otherwise uninhabitable. In short, future generations signify that we won't have screwed up humanity beyond all hope. Naturally, future generations can't communicate this comforting revelation to us. The fruits of our labor will be realized in their lifetimes, not ours.
So, getting back to the original question, why should our work serve future generations? In the spirit of being audience-centered, I shall address this question from a self-interested perspective. Future generations will be more affected by our actions than we are, just as we are more affected by the actions of past generations than they were. You can call it the butterfly effect, compounding, or whatever you like. Our work affects future generations whether we intend it to or not.
If we work either without regard to how our actions will affect future generations or suspecting that our actions are likely to cause harm to future generations, we decrease the likelihood of their existence. The grosser our negligence, the fewer future generations there will be. If the number of future generations goes to zero, then our generation is the end of the line. We end humanity. Do you want to take credit for that? No? Then get to work and stop bitching. The future is waiting.
Of course, if you are really, really successful at eliminating all future generations, there will be no one left to blame you. So I guess the takeaway message is, do whatever you like, but do it well.