I knew this was coming and I knew it was going to be really hard. Having another baby is one thing, but trying to move on and raise that new baby. On the one hand, it probably feels like a terrible betrayal of the memory of the missing child. On the other hand, you can't let this child feel punished for events that happened before he was even born.
I think people go through the same dilemma when someone dies. How can you justify being happy again (even for a moment) when they're gone and not feel like you're doing something terribly monstrous?