I've previously offered my take on why all opposition parties - including the Libs - should and will ultimately vote the Harper Cons out of power when given the chance. But I'll note that Don Lenihan's argument toward the same conclusion actually offers a reminder why there's reason for concern.
Whatever lesson one wants to take from C-51 and Eve Adams (among so many other stories), one can't claim for a second that they offer examples of Justin Trudeau and company valuing the support of progressive voters over cynical measures to appease the right. And there's been no evidence that the Libs have learned much in the meantime.
Of course, it would be for the best if the Libs decided that they should consider a "storm of anger...among friends and allies" as reason to think carefully about a choice. But in light of their track record, I wouldn't hold my breath - meaning that our best hope to get the Libs on board probably lies in political calculations rather than any newfound concern for progressive principle.