Poststructuralism by way of clownage
I recall the little French pierrot type clown figurine used to be in gift stores and teen girl bedrooms too (the more sophisticated clown motif than Bozo). I guess he's no longer in vogue either.
Strangely, I was one of those kids who was scared of everything in the whole world ... EXCEPT clowns. I liked clowns and never understood why others thought them scary. (I even had the pierrot doll that Katrina mentions above.) A contrarian even as an elementary schooler, I suppose.
A lot of people I know in my rough age cohort associate fear of clowns with one 1981 episode of Little House on the Prairie with a rapist in a clown mask ( https://littlehouse.fandom.com/wiki/Episode_717:_Sylvia_(Part_1) )
I agree with your larger point, but I think that clowns have had an “edge” to them longer than you give credit. Of the top of my head, Scooby Doo faces a Ghost Clown in 1969 ( https://scoobydoo.fandom.com/wiki/Bedlam_in_the_Big_Top ), Marvel’s Silver age featured a veritable parade of circuses of crime, Carnival of Souls (1962), and even going back to The Circus of Dr. Lao (1935) and Freaks (1932). I think the villainization of clowns was helped along by the fact that circuses are always inherently seedy—a bunch of itinerants showing up in town, known to be hostile to outsiders. I don’t mean to collapse carnivals (v. seedy) and Ringling Bros. B&B (less seedy), but even the classiest circuses have an air of the outsider about them and are covered in sawdust (maybe not Cirque de Soleil?).
As I said, I agree with your larger point, but I think clowns have long possessed an element of menage that made them fertile for recontextualizing, or would make the recontextualizing “stick” better than a recontextualized teddy bear, say.
Will clowns still possess this inherent air of menace in the future, when there are no longer seedy circuses filled drifting around the country? Like in the future, when clowns make their comeback?
So...you don't think John Wayne Gacy had anything to do with clowns becoming perceived as creepy?