If runways were like this from the beginning and someone said they're going to put two runways side by side people would say that was nuts!
"You mean I could be landing and there could be an aircraft right next to me taking off!"
Look at the following pic which is as close as it gets.
Photos: Airbus A320-231 Aircraft Pictures | Airliners.net
Now put that CX747 10,000' further away as it takes off from the proposed second runway.