Sinfest. Used to be a charming and funny daily webcomic about an eclectic cast of colorful characters getting into surreal and philosophical situations. Then one day in 2011 it suddenly swerved hard into radical feminism. I'm not anti-feminist myself, but the comic became obsessed with it -- literally every strip was related to The Patriarchy in some way and it became extremely preachy and boring.

I checked out for the better part of a decade, and when I randomly revisited a couple years ago it turned out that the author had transited the TERF-to-fascist pipeline and turned into an extreme-right antivax conspiratorial fascist loon, of the "teachers are secret pedos" and "the war in Ukraine is a hoax" variety. Super sad to see.