Human nature is largely fixed but different aspects of it are emphasised according the milieu in which the individual lives. The phrase 'The better angels of our nature' recognises this (comes from Lincoln's first inaugural address).

Pinker is of this opinion (he is against the blank slate) also the book does not say that there will be progress forever, I remember reading a statement to the contrary in it.

The interaction between the social milieu and the individual r.e. emphasising the better angels is hard to predict and we are undergoing an experiment with the rise of social media, which may or may not continue this progress.

The 'progressive' position is often associated with the idea that human nature can be improved by act of will. This is unlikely to work.