Simpsons has always backed liberal themes.
I stopped watching when I was old enough to recognize it.
In their early years, the Simpsons had some conservative writers, like John Schwartzwelder. Not coincidentally, there were some episodes in the 90's that were funny and weren't trying to preach some PC theme.
As the years went on, the Simpsons became cruder, more moronic, and more preachy politically. They went from being one of the only comedy shows worth watching on television to as bad or worse than the rest of the trash on TV about ten years into their run. The show is now almost two decades past its shelf date.
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