Substitutionary atonement?

I have a question (or a few related questions) that I'd really appreciate help with. The Bible teaches that Jesus died for our sins, that the Lamb of God "taketh away the sins of the world." Indeed, John teaches that he did this precisely out of his love for us. But then what would have happened if the Pharisees hadn't been so down on him, if Judas hadn't betrayed him, if Herod had staid his crucifixion? I mean, if Jesus had been allowed to live a long and prosperous life and to die peacefully in his sleep, then his intention to die for our sins would have been thwarted. Thus God needed people to be hostile, and not loving and accepting... God needed men to put Jesus to a cruel death, without which there could have been no divine suffering, and thus no supreme gift to all future mankind. No?

And furthermore, by this reasoning, we none of us have any grounds to judge, resent, or blame those who (in the event) were so unaccepting or callous or even cruel to Jesus, because had he found himself entirely among loving and gentle and receptive people, we'd not now have a saviour. And in particular, even if the simple historical facts were to justify thinking of the Jews as "Christ killers," they would only have been playing a role that God needed them to play so that he could substitute himself for our own sins. So the centuries of hatred (to say nothing of frequent slaughter) of those Jews' descendants, besides punishing for guilt by association, should rightly have been profound (if a bit ironic) gratitude.

I'd be grateful if people could help me make sense of this stuff. Thanks.