The Claim: G-d Forbids Human Sacrifice
When the LORD your G-d shall cut off the nations from before you, when you go in to dispossess them, and you have dispossessed them, and dwell in their land; take heed to yourself that you are not ensnared to follow them, after that they are destroyed from before you; and that you inquire not after their gods, saying: 'How used these nations to serve their gods? even so will I do likewise.' You shall not do so to the LORD your G-d; for every abomination to the LORD, which He hates, have they done to their gods; for even their sons and their daughters do they burn in the fire to their gods. (Deuteronomy 12:29-31 JPS)
G-d forbids human sacrifice!
In regards to the Tabernacle/Temple service, this statement is 100% correct: G-d forbids humans to be used as burnt offerings. But the Tanakh does give us a clear example of humans surrendering their lives to evil men... and G-d blesses the entire nation of Israel as a result.
Consider the story of Hananiah, Mishael, and Azariah.
Hananiah means "G-d is gracious".
Mishael means "Who is what G-d is?".
Azariah means "G-d has helped".
You might be more familiar with them by their Babylonian names: Shadrach, Meshach, and Abednego.
In the book of Daniel, we find these three young Jewish men elevated to positions of authority in the kingdom of Babylon. While in those positions, they faced a decision: worship Nebuchadnezzar's golden image or die.
But whoever does not fall down and worship shall immediately be cast into the midst of a furnace of blazing fire. (Daniel 3:6)
Millions of Jewish men and women were looking to them for direction. Should they do what Nebuchadnezzar demanded or should they refuse to bow and be thrown into the fire? The precedent these three men set would result in either spiritual death (idolatry) or physical death for the nation in exile.
Shadrach, Meshach, and Abednego chose to offer their lives:
"If it be so, our God whom we serve is able to deliver us from the furnace of blazing fire; and He will deliver us out of your hand, O king. But even if He does not, let it be known to you, O king, that we are not going to serve your gods or worship the golden image that you have set up." (Daniel 3:17-18)
The ruler of the world was filled with wrath and he ordered the furnace to be heated to seven times its normal temperature (Daniel 3:19). He ordered the three men to be bound and cast into the fire. After they were thrown into the furnace, they remained unharmed and came out without even the slightest singe. From that moment forward, Nebuchadnezzar sought to honor the G-d of Israel.
The Jews were spared by G-d's grace and the willing sacrifice of these three men.
Now... fast forward about 600 years. Another young Jewish man surrenders his life into the hands of evil men. The high priest prophesies that it is better that one man die for the people that the whole nation not perish. In this case, the young man is killed and the nation is spared an eternal spiritual death.
That young man was Yeshua of Nazareth. He died and was resurrected for his nation... and for people of all nations who follow him.