I agree, it should have been same server/battlegroup. but regardless why would people act like jerks, etc just because they can now press a button to join a dungeon/raid. Just because it made things easier doesn't mean it should have made the community worse. That blame lays on the community and no one else
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Yes there have always been trolls/jerks in the game, but that number skyrocketed after the introduction of LFG/LFR functions. I remember plenty of times in Vanilla and TBC people would communicate in the zones with others giving them directions on where to go or consistently forming up groups. I rarely solo quested in Vanilla/TBC. Yet somehow the introduction of the LFG/LFR equaled people no longer communicating, or at least not in a helpful way and being overall jackasses. As I've said in plenty of post just because Blizzard gave us access to more content with LFG/LFR doesn't mean the community had to go to hell... that was the communities fault, not blizzards. You still see some people helping, offering hints, etc in zones but more often than not if anyone asks a question now and days they get jumped on.