They were not against human sacrifice but they reserved it for times of great need.
This was one of the reasons they were appalled at Carthage.
Killing slaves was one thing. Killing your own children as a homage to your god was quite another.
The Romans didn’t have that many limits. Ask the Christians who were used as torches at garden parties, or were wrapped in fresh animal skins and fed to hungry lions and bears, or the thousands crucified with spikes through their hands and feet. Or the gladiator shows. The Romans were hideously cruel.