I don't think Marge considers herself conservative or liberal. And making her family go to church, didn't that episode air in the 90s when Simpsons was considered a bastion of amoral anti-family values and going to church was considered a social duty? Later when Lisa became Buddhist Marge supported her completely.
I have objections to taking away somebody's liberal card because they don't check every box you do. Marge wants a quiet, happy family life, empathizes with *everyone*, and supports anyone's right to live the way they want to. She's not liberal because she likes old school politeness and manners and wants everyone to get along? Gimme a break.
The character I've always thought was overrated was Homer, to be honest. Half is jokes are falling down or getting hit, the other half are that he's dumb, and he's got the running joke of being negligent to Marge's emotional needs (Until the last minute). In a way he represents the quintessential middle American, well intended gullible dummy. I don't dislike him, but I think the episodes that focus entirely around him are the weakest.
And also they need to seriously work on their secondary cast. All of them being one note semi-mocking stereotypes may have been expected in the 90s but it doesn't work in 2018.
Kind of ironic how Simpsons has reversed polarity on the public morality spectrum. In the 1990s it was considered immoral for not showing a wholesome family, and now for showing too many racial stereotypes and too wholesome a family.