One could ask the question of why God thought it was necessary to sacrifice His son anyway, since He could just make the new rules take effect. So it all comes down to the question of why He had a son at all, or why He does anything he does really, I guess.
Anyway, the argument was that if Jesus and the new testament never came around, then the concept of going to heaven or Hell for humans never would have either. Before that, you just died, or if you were one of a very few exceptional people you got called up to heaven. There was no eternal suffering for doing the wrong thing: you just died. With the new testament, you suffer forever if you do something wrong.
As for why the disciples didn't see it that way... well, they were on His good side I guess, so they didn't see it as a problem.
It's the old traditional churches that are actually kinda scary. We're the ones who say God doesn't actually do that much loving, comparatively speaking, and bad things happen because he wants them to.
Oh, yes. The church I still go to (mostly unwillingly) is of this variety. God kills babies to keep them away from abusive parents, for example. Oh, and the problems Joe Biden has had with his family's illnesses and such? Yeah, he shouldn't have been a liberal or that probably wouldn't have happened. Also, the Pope is going to bring about the new world order and make us all worship Islam, and gay people are stealing babies from straight couples. There's also murmurings of FEMA camps out in Texas that Obama is going to send people to, and 30,000 guillotines being bought by the government to behead dissenters.
I wish I was making that up. I'll also stop before I derail the thread on that, since I know that's not representative of Christians as a whole. It's just amusing.