I can see two reasons for the Liberal party to move to the center:
1. It's appropriate in the current economic context.
2. It's politically expedient.
Argument 1: We are moving into a recession, and we need a steady fiscal hand, not new expensive progressive policies.
Argument 2: With the left split across four parties, it may be the only way to separate ourselves from the pack.
We can't give up our principles, and we can't give up on environmental policy, but in a recession it's important to prioritize the size of the pie rather than the size of the slices. Improving the size of the slices helps those who still have jobs, but improving the size of the pie helps keep people from losing their job.
I'm not convinced by my arguments, but I think this sort of question should be on the minds of all Liberals as we head into a leadership race.