Actually, I support both of these cultures to execute their respective moral codes internally.
The problem becomes if it spills outside their populace and ensnares innocent people, like we see in A Taste of Armageddon. You can't enforce your moral code on other cultures.
So it's perfectly all right to allow other cultures to practice human sacrifice because "that's their culture", just so long as it's their own people that they are killing?
Doesn't fly. Not for one minute.