@oristarA,
The word "venerable" is subjective. I suspect that the people in this culture don't share your opinion that this tradition is horrible or dark any more than we see our forms of justice as "horrible or dark".
You are looking at things through your own cultural bias that has everything to do with where and when you are born and how you were brought up. Some cultures will see this as horrible and dark. Other cultures will see it as an example of justice and fairness.
Obviously the writer brings up this particular example to be shocking to the people who will read his book. The word venerable is chosen to highlight this effect... this is an example where different cultures view an act in very different ways.
I don't consider this an example of "sarcasm". He is using a word to make his point in a strong manner... and the word made you react emotionally in the way the author intended.
I thought Sam Harris argues for a form of science-based moral absolutism, doesn't he?