This is an ethically neutral activity. The mere act of transforming a device into such a computer doesn't add or remove any nefarious goals, if you have those goals, you can get another device intended to be a Linux computer and still accomplish them (and it would be much easier). If the transformation is done in contravention of the owner, it's bad, but it sounds like from the article that the ISP has written it off and in any case, they say they are doing this nondestructively.