Those failures are enough to make many lefties want to have nothing to do with the NDP. But I would suggest the failures of the NDP are a particular form or manifestation of the general failure of the left. Whatever you do as an activist, you are still part of that general failure of the left- it is just a form of failure that you are more comfortable with.
Activism as we've come to know it contributes to a general paralysis of the left precisely because it is comfortable with any assurance that comes along promising to do at least something, anything, from a very long and immediate 'to do' list. The rush to grasp at any shiny object dangled before us places the left in a deplorable bargaining position from which to approach power. After every protracted struggle, every tenuous half measure granted from on high causes us to thunder in toward the centrist dead end zones, where we find them busying themselves with illusionary DIY improvements to the dilapidated edifice of capital. All the left manages to do as a result is to produce contenders vying for positions as better managers of the existing catastrophe. Essentially, our contemporary version of the left asks for too little and receives even less for its trouble. If temporary measures and petitions to the ruling class suffice to convince representative activism and the left in general of their usefulness, they would be better off starting from a position which maintains that the current political and economic structure must simply go, mobilize to that end, and then table their demands.