...if we hope to maintain a humane, democratic society.

I would maintain that we (USA) do not have what qualifies as a humane and democratic society. We may have come close a few decades ago, but things have been decidedly downhill since the 'Reagan Revolution'.

The trends of wealth accumulation, poverty and injustice are plainly negative. At present we likely have available the most energy per-capita that will ever be available (some figure the peak of per-capita energy was passed ~1989). Given this, how are these trends likely to be reversed. How are we going to fix our deteriorating infrastructure, house our homeless, provide health care and education for all in a future with less energy available? Especially considering the extra energy that will be taken to make the post fossil-fuel transitions?

Optimistic back-of-envelope calculations will mean nothing until these negative trends are seen to be clearly on the mend.