But, when I'm thinking in List[Any], I expect to be working on the Monoid for List[Any], not the Monoid for List[Int]: things like special-casing List[Int] are

But, when I'm thinking in List[Any], I expect to be working on the Monoid for List[Any], not the Monoid for List[Int]: things like special-casing List[Int] are exactly what make programming languages difficult to learn and use.