The Liberals perhaps can't afford not to fight, but they could conceivably undercut themselves (and help Moe) if their response seems irrational.
This is precisely what Moe is counting on. The Liberals shot themselves in the foot when they tried to buy Atlantic Canadian votes by exempting heating oil from the carbon tax. That reenergized the opposition to carbon tax and gave the Conservatives a great stick to hit Trudeau with.
I hope the Liberals err on the side of ~~public opinion~~ caution and find a way to punish Moe's government without seeming draconian.