I would argue that a strictly rationalist or at least secular morality should be applied given the sheer religious or spiritual diversity of the global population.

And regarding your latter point,it is as you say simplistic - much like the proverbial bacterium on an agar plate, our growth imperative will destroy our future if we overrun the bounds of our environment. I think we will see the issue become more important as the consequences of overpopulation (with respect to resource consumption and carrying capacity) begin to bite.