Some neopagans would prefer to believe that human sacrifice was never a part of ancient paganism, but of course it actually was. The archeological, historical and literary records provide far too much evidence of this for any reasonable person to doubt it. Some cultures practiced human sacrifice as an occasional ritual act of great power, an exchange between humanity and the world of the divine in which a thing of great value (a human life) is offered up in anticipation of a great reward. Other cultures practiced human sacrifice on a massive scale, slaughtering hundreds of victims at a single ceremony. These acts are repugnant to us today, and with good reason.
On the other hand, the callous violence of human sacrifice is by no means a feature unique to ancient paganism. What about the auto-da-fe, the central public ritual of the Spanish Inquisition, in which “heretics” were forced to publicly confess before massive crowds before being burned alive? If this is not a human sacrifice, the distinction is an academic one.
The ancient Romans professed to be horrified by the Gaulish practice of human sacrifice, but they also threw people to the lions for public entertainment. Modern atheists would see human sacrifice as one of the evils of religion and superstition, but atheist totalitarian regimes murdered millions of people in the name of ideology, so what's the difference?
The practice of human sacrifice in ancient paganism should not be denied, because it's a historical fact. But it also shouldn't be blamed on pagan religious ideas- whether pagan, Christian, atheist or anything else, humans still have a lot to learn!