I used to be mouthy. It was all to do with being a northerner and from Manchester, which was suddenly a big deal when I was in my 20s. When I read some of the interviews I did back then, I cringe.
The modernists started with the assumption that science is the only source of sure knowledge, that nature is all there is, and thus that morality is merely a human invention that can be changed to meet changing circumstances in an evolving world.