"If the private sector *had* built it, in order to make a profit they would have had to either charge higher fares or provide lousier service. "

Or the private sector companies would have looked at it and said "This doesn't make any sense, we're not going to build it until there is a legitimate plan in place".

... ohh wait, that is exactly what happened.

It was only after the SNC Lavalin said that the plan made no sense that Metrolinx went ahead and implemented it.  Actually Metrolinx implemented an even more expensive plan then what SNC Lavalin rejected.