Although sidechains are interesting technologically, they highlight the design conflicts that arise when you try to impose a technology solution to a monetary problem. For example, confidential transactions does let you cover the tracks of a particular transaction when seen from a granular perspective. But what impact does it have at a holistic monetary level ? An adverse one - majorly so - because in trying to solve a privacy problem it creates a huge fungibility problem. The logic of it is similar to washing your clothes in an acid bath to remove a coffee stain.