The article reads a little alarmist honestly. They have created a low bandwidth mesh network for mostly IOT devices. I don’t get how this is suddenly compared with sharing internet. The later of which, Comcast actually did and does.
Far be it from me to defend Comcast, but it's not equivalent in the slightest. Comcast creates a separate network, with a separate IP, using their cable modem and the DOCSIS bandwidth available on their network. Its third-party usage does not count against your data cap, and any nefarious usage would not be associated with your own account and possibly subject you to civil or criminal sanctions.
Devices can only talk to specific Amazon APIs (which then hand the request to manufacturer APIs) with Sidewalk, they don't get to arbitrarily use your internet connection either.
Here in the UK, BT does the same thing and nobody seems to complain. If you're a BT customer you can use your own data through somebody else's router. Maybe actually giving something in return is the answer for Amazon?