The problem in that argument is that the Liberals aren't Left or Progressive. They are the centrist "Natural Ruling Party" whose main aim is staying in power. Sometimes they pretend to be progressive, and the voters fall for it every time. Then they rule from the center/right. They manage this by routinely lying on the campaign trail.
 
If you are progressive, vote NDP. If you are conservative vote Conservative. The Conservatives at least do what they said they'd do. Give the NDP a chance and they might too. Breaking promises is bred in the bone for the Liberals.