Clinton negative ad

James Forman's comments on Clinton's new negative ad in Wisconsin (www.youtube.com/watch?v=HzGbj_ERlJ0), which seems rather tame to me:

A few of you emailed this morning to say that Clinton would go negative because she realizes that she loses if she allows this to be positive.  I guess you're right.  BTW, the ad seems reasonably effective, but I don't know much about the history of "he is scared to debate me" ads so I don't know if historically they move voters.

Curious to know what folks think of the debates issue that Clinton's ad raises.  I guess for the candidate with less money it is free advertising and Clinton debates well so I see why she wants them.  Obama has more money, doesn't debate as well (though getting better), connects with voters better in speeches and town halls, and would probably spend time doing that not debate prep.  So I see why he doesn't want them.  But beyond who benefits, is there a principled argument here one way or the other?  I know I feel like 18 debates is enough, but maybe that is my Obama bias coming out.