My title caught your attention.
I won't suggest that Layton and Harper should not be debating each other. I just wish to remind Layton that the NDP is still not in the top two positions. Those belong to the Conservatives and Liberals. Layton may wish to debate Harper. He will get a chance in the two debates. However, Harper may not really care about debating Layton. If Layton can shut May out of the debates, then a Conservative leader can do the same with an NDP leader in the future. Harper's target is Liberal leader, Stéphane Dion.
Because of Canada's far from perfect First-Past-the-Post voting system, Layton is just the leader of the fourth party. He's only one step above Elizabeth May and two steps below Harper. Layton is just a pip-squeak who doesn't deserve the attention in Harper's eyes.
Layton should rethink is position about May participating in the debates.