Every simpsons fan I know watches seasons 2-8 all the time in any given year. The episodes don't have any real continuity so they can be viewed in any order for laughs.
>The tone changed over the course of the show
That is really the only argument rational simpsons fans are making. Anyone who suggests that the new show is TERRIBLE only feels that way because they're comparing older episodes which from start to finish were pure gold vs new ones which are merely funny.
It's unfortunate that you have such a negative reaction towards people critical of the newer episodes to say things like "the simpsons sucked and has always sucked." Clearly you enjoy the show on some level I don't really see why you would say that unless you were being intentionally inflammatory.