I think a couple people touched on this, but there is a benefit to "sentience". Theoretically, some smart individuals can realize this kind of stuff, influence human societies and "someday" we will have a culture that encourages long-term, sustainable thinking -- from childhood. The brain is pretty malleable and many "instinctual" reactions that have bad consequences can be weakened. In other words, someday we might have a "star trek" future with no (well, minimal) poverty, pollution and so forth. But the abyss will always be there where we (as a collective) could fall back into the "bad", long-term destructive behaviors.

Or maybe I'm just trying to counter your pessimism with unsupportable optimism. :)