I think the big difference is this is the first time that people are genuinely questioning the viability of our species' future.

In the past, however bad things might be, there was a plausible hope that the future would turn out acceptably better. Not, materially, environmentally and in terms of ethics and human rights, we can see very clear signs of a downward slope stretching out ahead. And we have the time and access to the information to pause and consider that. And are increasingly used to the idea of choosing our own pathways, rather than simply following a social preset.

Our prescribed part in the ongoing story of humanity no longer strikes us as either inevitable, or even desirable.