CPP is a pension plan, and the other pension plans treat it as such. For example, my pension contributions for my working life were adjusted for CPP contributions, and my pension is adjusted - at 65 my pension goes down by the amount that they expect my CPP to start up at. This is basically the same financial strategy as maternity leave, where part is your work leave and part is EI. So any elimination of CPP has repercussions for financial planning. This is why the changes are introduced slowly and there is always a grandfathering element. Anyway, the government a few years ago did bite the bullet and make changes so that it should be self-financing for the long run. But these discussions act as if the CPP is a hand-out - it is not, everyone getting CPP has paid into it, just like they pay into a pension at work or their RRSP. Given the lousy Canadian track record at taking advantage of RRSPs, it is probably good that people have to do some pension savings because of the CPP, even if it isn't a lot.
OAS, on the other hand, is a "freebie", but a claw-back one. I am sure the cost of OAS for low-income seniors is less than the cost of social services they would need if the OAS were not there. Same for the GIS.