This is a very poor post, full of almost comically bad arguments and rationalizations.

One way around this is to find some robust metric that most people would agree indicates guilt. One such measure, I believe, would be murder rate. If people in different cultures vary in the guilt they feel for committing murder, then this should hold them back and show up as a variation in the murder rate.

This borders on the idiotic. Since the author doesn't understand the obvious huge problem that it's impossible in this case to control for other factors, which are likely to be overwhelmingly important, none of their arguments should be taken seriously. It's the sort of cluelessness that makes it likely that in all other cases the author was merely fishing around for plausible correlations, rather than tried to judge the issue or build a convincing argument.

There is evidence that it [the distinction between modern and traditional] is caused by inbreeding and the accumulation of genes for familial altruism...

What evidence?

Since studies on this are non-existent as far as I know

Oh, OK.

– no doubt for political reasons

But political reasons didn't prevent people from publishing studies on race and gender and IQ, or the whole of evolutionary psychology from existing.

Really, the whole thing is very, very bad, and that even before they get to "gene variants for guilt proneness".