I think people can't disentangle your factual claim from what they perceive to be the implication that we shouldn't be careful when trying to engineer AGIs.

Hmm - no such implication was intended.

It seems clear that something like progress has happened up until the dawn of humans; but I'd argue that it reached its zenith sometime between 100,000 and 500 years ago, and that technology has overall led to a downturn in the morality of the common man.

The end of slavery and a big downturn in warfare and violence occured on those timescales. For example, Steven Pinker would not agree with you. In his recent book he says that the pace of moral progress has accelerated in the last few decades. Pinker notes that on issues such as civil rights, the role of women, equality for gays, beating of children and treatment of animals, “the attitudes of conservatives have followed the trajectory of liberals, with the result that today’s conservatives are more liberal than yesterday’s liberals.”