Roko exaggerates. It's only 377 pages and written in an accessible style.

It summarizes the ethical literature on moral realism, and takes the irrealist view that XML tags on actions don't exist, and that even if they did exist we wouldn't care about them. It then goes into the psychology literature (Greene does experimental philosophy, e.g. finding that people misinterpret utility as having diminishing marginal utility in contravention to experimental instructions), e.g. Haidt's work on social intuitionism, to explain why it is that we think there are these moral properties 'out there' when there aren't any. Lastly, he argues that we can get on with pursuing our concerns (reasoning about conflicts between our concerns, implications, instrumental questions, etc), but suggests that awareness of the absence of XML tags can help us to better understand and deal with those with differing moral views.