I find find this either Punk or Prog attitude after all these years most bizzare as well. I can understand such an attitude during the time of Punk as it was a reaction to what had gone before. But years later it is a bit of a bell ends attitude. In fact I feel cheated a bit by what a closed mentality did to my own listening tastes as I grew up. It took me years to get over the year zero attitude.
Another example is during the 90s I was talking to some Mod throw back and he was going on about how he hated Rockers. Well you could have understood such attitudes during the 60s, when any new movement has a either for or against attitude.
Music is a multi-woven tapestry type thing and it is a bit sad when only one thread is used to define peoples tastes.