People after Fermi have spent a great deal of time on this very issue. For a number of reasons that I won't go into here, it turns out that one can demonstrate that grabbing resources as fast as you can is critical to survival in the long run and that any highly developed and rational society would HAVE to expand outward at a very fast pace. The calculus of it all points to advanced civilizations dismantling natural resources at a dizzying pace. The rational solution when the number of civilizations is one is very different from the rational solution when there are many civilizations.
This is essentially a case study of trying to predict what an alien civilization may do based on our current understanding of science and historical development. My speculation is that a highly advanced civilization would likely operate under different constructs than us because of their success in solving problems that we have yet to even contemplate. Kind of like our own development over the centuries. But just because our only very recent attempts to pick up ET signals have not yielded results so far does not mean that intelligent ET life does not exist or we won’t detect their signals in the future. With any luck, people like the Radio Astronomer with ever more sensitive equipment and detection techniques will one-day pick out ET signals from the noise of space. Fermi's arguments are too one dimensional to take seriously.