Does Lakoff have robust experimental data validating and testing his ideas? Or is this a whole bunch of posturing that validates leftist intuitions but isn't actually based on anything?

Because this is pretty strongly at odds with The Righteous Mind (Haidt, 2013), and that does have a lot of experimental data validating the basic ideas.

In brief: cruelty is not the point. Indeed, leftists misunderstanding the point is the point of the book. (Right-wingers misunderstand too, just a bit less.)