I think the idea is that if Jesus had appeared before God took to drowning the earth and otherwise decimating it's population, then you could argue that Jesus wasn't necessary, as man at that time hadn't yet demonstrated his sinfulness sufficiently to make the savior maximally impactful.
If God had sent in Jesus immediately the first man sinned it would have saved a lot of bloodshed, but wouldn't have done so much for god's public relations.
That doesn't really answer the question about why God created a sinful race, being all-knowing, and knowing that he'd have to punish them through slaughter - and then send Jesus to make an example through him, by making him suffer tremendously, despite not having been sinful himself. He sacrificed himself, the decent fellow that he was - but why did he have to?
Also, people are still being rather nasty and sinful - so torturing Jesus didn't make the slightest difference. AFAIK, we've had quite a lot of torture and mass-slaughter BECAUSE religious people don't agree with each other, and apparently - it's A-OK to kill each other for that reason, based on a surprisingly widespread interpretation of the divine word.
Obviously, we're not smart enough to interpret the crystal clear teachings of the Bible, so we're going to kill each other. But is that our own fault for being so stupid? Are we being willfully stupid and do we really enjoy killing and dying?
Again, it's obviously something you'd have to be a Christian to understand.
I've never been comfortable with other people suffering - and if I could have my way, people wouldn't need to die and suffer constantly. I felt really bad just this morning when I drove right past the corpse of a cat with the lower body maimed on the freeway. I don't really understand why the cat had to go through that - but I guess there's a lesson there somewhere.
If the lesson is that we should not drive cars, then I wonder why we're capable of creating them in the first place? If God doesn't like that kind of suffering - then why is the lesson itself more important than the suffering of innocent animals?
How many people would have died and suffered as a result of not being able to drive to the hospital, if we're not allowed to drive cars?
Why are cats made without the ability to stay out of harm's way?
We can drive cars, but only if we're perfect drivers who can't make mistakes? People are still Christian if they make a mistake, though, so all will be forgiven - but the cat still suffered.
The cat itself was sinful? It didn't read the Bible thoroughly enough?
So many things I don't understand.
But I'm not a Christian, so obviously I just don't have what it takes to understand all things divine.