Justified or not (and I certainly don't think it is), don't you find it odd that some fans (a vocal minority, to be sure) would rather see Toronto fail than see their own team succeed?
I have a buddy that is a self proclaimed Habs fan. But he never talks about Montreal games, their players, or anything. He only mocks the Leafs. He actively teased me when Toronto fell to Boston, even though his (supposed) team missed the dance completely. The threads about cup predictions are filled with comments saying "anyone but Toronto".
And here we are in a thread about an incredibly entertaining young star player, and no one writes a single compliment about the guy. No neutral fans popping in just to say they really like watching Marner, or that they wish they had him. No. Nothing but jokes about our stars getting overpaid, and the team being doomed to fall apart. Would it look like this if the thread were about Clayton Keller? Did it look like this for Johnny Gaudreau?
I'm telling you (whether it's justified or not) there is a group of "fans" that hate the Leafs more than they like hockey.