I would say each fan base is coming from different perspectives and places.
I would expect Y fans to feel very similar as Ute fans when they got the PAC12 invite.
As a Ute fan, at first I wanted the PAC12 to stay together but once Oregon and WAS left for the B1G, I was then relieved that the U had made prepared and made contingency plans to act quickly and go to the XVII. Now I'm still process the move and all the possible different implications it has for the U but it is slowly becoming more real and exciting.
For example, the PAC had more "prestigious" (USC, UCLA, Stanford, Oregon & WAS) schools but those Cali schools didn't always have the fan support, whereas in the XVII almost all the schools have a ton of fan support, which will be exciting, so there's trade offs like that.
Keeping the rivalry and trash talk aside for this post, I can understand why the Y fans were taking joy in the PAC12 mismanagement, and then not being happy that the U got the invite and accepted so quickly at full revenue. BUT I would hope it didn't take away from the joy of now being in a P4 conference (yes that last part was hard for me to type with out a little joking trash talk).