I think the point is that Morality can very simply be an evolved human trait due to the massive second and third order effects that derive from it or the lack of it.

Let me put things this way: psychopathy is a condition people are born with, were they are unable to empathise with others so amongst other things they don’t feel the hurt of others and are thus capable of inflicting great hurt to others, lie and do all sorts of socially-reprehensible things without feeling a shred of guilt. In practice they will do what’s best for themselves with no consideration for others except for the purelly rational “can they punish me if I do this” (in simplifying all this a bit since psychopathy is actually a range rather than simply an Yes/No thing).

Anyways, around 3% of people are born high in the psychopathy spectrum. Now, if psychopathy is “doing what’s best for yourself with no consideration for others, no guilt, no conscience to be weighted on”, which one would expect is the best possible survival and reproductive strategy there is, why hasn’t that trait not dominated and human evolution led to 100% of people being born psychopaths?

My theory is that societies with too many psychopaths collapse, removing the psychopaths from the genetic pool.

How would that be. Well, they’re pure takers - why tire oneself by making if you can get away more easilly with taking - and they’re not good at cooperation (mainly because when others spot their character, they don’t trust them and don’t want to cooperate with them), so any society with too many psychopaths is less productive, has less resources available (too many takers too few makers), it stops evolving, can’t properly organise a collective defense system and eventually gets overwhelmed by some other society without such problems.

This last bit is just my theory for why, but certainly the part that only 3% of people are born like that is a pretty good indication that for some reason an amoral behaviour in humans is not a winning evolutionary strategy even though some might think at first sight that it would be.