Zoe said:
If it was simply about capacity then high speed wouldn't be as important but clearly this is about high speed also.
The reason it has to be fast is because higher speed = more paths = more capacity. That's the main reason for the line's higher speed. If the current WCML could be upgraded to HS2 speeds, we wouldn't be having this problem.
Even if such capacity is not vital right now, don't forget that the line is only due to start running in about 20 years or so. By then the amount of rail traffic in general will have increased substantially. Think of the line as future proofing for capacity needs.
I lived in the Chilterns for ten years, and my parents still live there; there's some beautiful countryside right on our doorstep. In that ten years, the number of cars on the roads increased dramatically and is still increasing, as more houses are opened on numerous greenfield sites. In my eyes, this is of much bigger concern than HS2, because it not only affects larger chunks of land but also impacts local infrastructure (congestion in the morning is terrible). Yes, the Chilterns is an AONB and efforts should be made to preserve it, but HS2 is a two track railway line; it's not going to lead to half the Chilterns being slashed and burned. (Although I seem to recall the anti campaign saying that the tracks would need to be 70m apart to prevent turbulence issues! :roll:

)