Sidewalk isn’t a wifi network that people can just connect to, it’s a LoRa radio. A low bandwidth, long range protocol. Devices connecting need to be pre-registered with Amazon, and can only communicate via an endpoint in AWS.
Even if someone somehow created a device for arbitrary web browsing via Sidewall, and put up with the incredibly slow connection speed, combined with strict limits on how much bandwidth can be consumed, all they get is a VPN immediately traceable to their AWS account.
I am not sure I understand why one is a concern while the other isn’t.