The dangers of expanding CPP is what you saw with the Caisse de dépôt in the financial meltdown. They lost a third of the wealth of retired Quebecers because it's a compelled government savings program with a single investor, essentially. Instead of having many investors investing their own retirement savings as prudently as they can, you have people taking big risks and everyone suffers.
On November 6th, 2012. See this statement in context.