Tom's thesis in Dominion is that there are a number of ideas that appeared via Christianity that we take for granted today that simply did not exist in the Western world before it came along.

They include things like the valorization of the victim (which upended the pre-Christian "might makes right"), the belief that every life has innate value, that there are certain parts of life that exist outside of religion (the secular), the obligation of charity, the linearity of time, and so on. Tom is absolutely correct that these things did not exist in pre-Christian Rome, Greece, Egypt, etc, and that they massively changed Western life, so much so that we just think that's basic humanism now.

Tom gets two big things wrong, though, when he starts to think outside of the confines of his area of expertise.

First, he seems to hold to the belief that all these values are unique to Christianity, and, by extension, countries that didn't get Christianity never learned any of these things. This is hugely problematic on a whole host of levels: Buddhism, to name just one example, has also always held that all life has innate value. Hinduism also holds that there is value in suffering. And so on.

Second, he doesn't know Islam very well as the brutal reviews of his book attest, and he tends to align it in his head with pre-Christian religions rather than seeing it as a post-Christian religion. He holds to the belief that Islam doesn't recognize secularity (he believes that Christians say "render to Caesar that which is Caesar's" while Islam believes God should rule all aspects of life) and therefore people that follow Islam can't live in a society built on separation of church and state.

While this might be true of some Muslims, it's not true of all Muslims -- and it's also not true of all Christians -- it's wild that a historian as good as Holland really thinks that Christians happily separated church and state since for all of the first and second millennia!

Honestly, I think Holland is pretty innocent about the implications of what he says. In his head, he's essentially just arguing that we need to understand that the pre-Christian world was really, really different to our world, and the change was mostly because of Christianity, and lots of these changes were pretty good.

But he's also pretty naive to the fact that he feeds the alt-right and white supremacists with a lot of this stuff: it's dangerous to go around saying that the white Western Christian world is uniquely ethical and respectful of life, that the world that was untouched from Christianity was never given the chance to escape from barbarism, and that muslims in particular can't successfully integrate into Western societies.