At least as far as Judas is concerned, there is an exact answer in Matthew 26:24:
For the Son of Man must die, as the Scriptures declared long ago. But how terrible it will be for the one who betrays him. It would be far better for that man if he had never been born!"
I've also heard it phrased "but woe to him through whom it comes."
That said, God is sufficiently great to turn even evil events to his purpose. Joseph says as much in Genesis 50:20:
"As for you, you meant evil against me, but God meant it for good in order to bring about this present result, to preserve many people alive. (NASB)
Finally, Romans 8:28 (a verse that it should be illegal to quote without a license!) hints at the same, saying:
28 And we know that in all things God works for the good of those who love him, who have been called according to his purpose.
Disclaimer: I never have, nor never will tolerate any form of anti-Semitism based on "Christ-killer" propoganda. As a German student who won a trip to Germany for my study, I was personally sickened when, as part of a class, I had to watch a Nazi propaganda film, that pushed this line of thinking. The question asked for a justification. I am providing that argument, even if I completely disagree with it.