The point about the Bears and the Vikings and our chants at them is a valid one, but for me the biggest difference is the total "beat-down" that team, and more importantly, their fans have endured. I recall sharing on this forum my visit over to a Lions board on the week preceding our first game against them, with an intention to join the site and talk a little good-natured "smack", along the lines that Pack93z and myself do year-round over at P.P.O.
The difference between P.P.O. and the Lions site is night and day. No Packer smack amongst them, no wishful thinking, just a beaten down fanbase resigned to the fact that the team they love is getting royally screwed over by ownership/management. I truly felt sorry for them.
I also tried to join a Bears website, after having been warned that they are a bunch of arrogant prick assholes. I did a lengthy introduction, told them I was also a member of P.P.O., and wanted to engage in some discussion, bringing some Packer fan perspective to their board. I did the same thing when I initially joined P.P.O., and was warmly welcomed.
The jerks on that Bears site laid into me with a whole series of childish nonsense. I immediately removed the URL from my "favorites" and have not been back. They are sort of easy to hate on, and I saw no evidence of them feeling "downtrodden", so I consider them "fair game".
Perhaps my "class" is selective, perhaps nuanced to a degree that is hard to discern. My best analogy is that if a pit bull comes at me, I will do my best to kill that dog. If a poodle shits on a rug, I reckon I will clean it up, scold the dog, but I'm not gonna kick it or anything.