Well, fans be fans. Canadian fans even more so and among Canadian fans Montreal might have the best and the worst... But yeah, it's hilarious and/or infuriating at times. If you ever feel like this place is bipolar or overreacting to a bad game or whatever, go stalk the boards of pretty much any Canadian team and see what it's like when things are not going well.
I think it's in part just the level of passion/sense of importance for hockey and the scale of it. And as usual, often times it's of course not the same fans, though following the discussion around Laine, I was surprised in how many cases it actually was
You could go through post histories of some people and find fans who went from "wouldn't touch him with a 10-foot pole even if we got him from free" to "wow a what a steal, I bet he's gonna score 50" or something like that...