If the bible says that Jesus was slain before the foundation of the world, then we are being told that our omnipotent, omniscient God created this world knowing exactly what was going to happen.
In fact, these things we are discussing are appointed to take place as clearly as if an appointment in a calendar had been set.
Judas was going to betray Jesus.
All prophecy is proof that appointments have been made.
Jesus had to be born.
It had to be in Bethlehem.
He had to be betrayed.
It had to be for 30 pieces of silver.
It had to be by a friend.
It had to be by one of his leaders.
Judas was the guy.
And if God brings about good with all of that, then who are the sheep to argue with the shepherd about which deserving sheep get slaughtered.
God spoke through the prophets and he did not say it HAD to be that way he said it WOULD be.
God being omnipotent, and omnicient could see that it would.
That does not mean that he made it so, and that no one had any choice but to do so.
*************
What does that have to do with the Immaculate Conception?