The Liberals must be spooked about being seen forming agreements with the NDP, because the surest way to block a Conservative majority in the next election is with a limited non-compete agreement. Speaking strictly on electoral math, theoretically a full non-compete would have put Stephane Dion in government in 2008, assuming that 100% of NDP-Liberal voters cast a vote for their coalition counterpart. Even a limited non-compete in say 20 Tory ridings would in theory maximize the seat counts of both parties.
Why would the Liberals want to avoid any non-compete agreement with the NDP? Probably for the same reasons that I would write a blog post encouraging them to do so, because the Liberal right flank is vulnerable. Whenever the Liberals shift to the left, they lose support in the center. The center is where the greatest plurality of voters exist. If Ignatieff thinks that the next election is going to be won on the far left, bring it.