I guess because Conal explains the type inference limitation in question using mathematical terminology, it's tripped the author's "cargo cult mathematics" dete

I guess because Conal explains the type inference limitation in question using mathematical terminology, it's tripped the author's "cargo cult mathematics" detector, but it actually sounds more like a software engineering concern. They want to avoid having new instance declarations break existing code (inferences), which seems like a reasonable property to not want to have from a software engineering POV. It makes more sense when building from code files than in interactive mode.