While that may be true, would they view propping of Harper to be more damaging to future election success that working with the other party. 
  
Well you can always spin giving the Conservatives support as "Just doing what the voters showed they want" GIven that both the NDP and Liberals want to position themselves as the alternative to voting Conservative working together that closely would do more damage. **** it up and people will turn around and put the Conservatives right back into power, do it well and the senior partner would get all the credit for it and the third party gets forgotten. I see supporting the Conservatives provided they get concessions as the best bet.  
  
Get some concessions and then abstain from voting. Get what you want and not vote for the Conservatives would be a win-win from an opposition position.