Why did the ancients engage in animal sacrifice? I'd previously pointed out that Ovid claimed that the gods could be propitiated with mere incense. If this view were widespread (did anyone maintain the contrary?), then one must ask why the religious colleges went to the additional bother of sacrificing whole animals, and why they distributed the meat of the sacrifices to the people.
Given that these sacrifices were conducted as part of a state religion, given that the administration of the state religion was conducted by priests who were always members of the socio-political elite, given that the socio-political elite was very often irreligious (particularly in the middle to late Republic), and given that the political status of this less-religious elite derived partly from the services that they could offer to the Roman people, it seems likely to me that the animal sacrifices were continued for political functions, long after they had ceased to have any real religious significance for those who sponsored them (i.e., they were a holy barbeque).
Since the "holy bbq" characterization is contingent on at least four separate assumptions, there must be many cases where the assumptions do not hold and the characterization may not apply, including private sacrifices of animals and sacrifices in the pre-Hellenistic world (when the political elite in Rome seemed more religious).
No, I don't think that the lares and penates served a purely decorative function, particularly since they weren't displayed in that way. More broadly, I'm not arguing (like Malinowski) for a functionalist explanation for all religious practices. But I think they have their place. While the lares and penates weren't typically used for decoration, some images of the gods were purely decorative and non-religious. Moreover, to point out the obvious, ordinary people and slaves typically could not afford to sacrifice oxen, sheep, and pigs to hand out to their neighbors. Consequently, the beliefs of slaves and the poor are irrelevant to the conduct of the state religion.
What you taught schoolchildren is simplistic and misleading. Sometimes, you CAN apply "our" mores and morals to the ancients because we inherited those mores and morals from the ancients. Sometimes, you can't--because we've either innovated new norms or inherited other norms that came after the ancients. To know the difference, you could have taught them, one must study intellectual and social history. It's really too bad that you had a perfect opportunity to introduce children to the idea that our modern behavior and ideas owe their existence to the ancients, and instead you expressed the same gutter relativism they hear everywhere.
... computational engine. You're thinking of the Antikythera Mechanism.