Yeah, you pretty much nailed it. The general idea is that if a civilization reaches a certain level of technological development, we should be able to detect it. But we haven't, so why? Thus the postulate that there may be certain natural and technological barriers that act as filters and either allow a civilization to progress or die out. Perhaps it is exceptionally rare and difficult to reach our present level of development. And even more rare to get over our present challenges, climate, resource depletion, political or otherwise, to become technologically advanced enough to spread out to neighboring planets/star systems. It probably gets easier to create extinction level risks as tech becomes increasingly powerful and distributed.