I’m so glad you wrote the island piece!
This is spot on.
Elizabeth Kolbert, in her book The Sixth Extinction, talks about gestation period being a key factor in cases of megafauna extinction at the hands of humans. Even a slight increase in predatory pressure (from say, humans) can be enough to cause a species with a long gestation period to collapse over time.
Leading to that unnerving bit you mentioned — mainstream ideas may be surprisingly prone to total collapse when increased pressure is applied. Pressure, that as you laid out, was not routinely applied (or was at least more easily controlled) in the past due to the checks of public discourse keeping fringe ideas to the fringe.