a lamb/lambs to the slaughter
like a lamb to (the) slaughter
Without concern for what is to come (because one does not foresee the trouble ahead). This phrase comes from the Bible. When I did business with Michael, I was like a lamb to the slaughter—I had no idea he was such a criminal mastermind. The poor kid and his defense team weren't aware of what the prosecution had in store—it was like lambs to slaughter the moment the trial began.
(like) a lamb/lambs to the ˈslaughter(do something or go somewhere) without protesting, probably because you do not realize that you are in danger: When the war started, thousands of young men went off to fight, like lambs to the slaughter.
Slaughter is the killing of animals for their meat.