Also, this does not excuse the fact that they made it opt out. If it was opt in and new devices came with it... maybe...
also, as far as illegal traffic and stuff: if the traffic goes through the amazon device, wouldn’t the isp see traffic that goes only go random amazon datacenter ? at that point they would ask amazon about it (hopefully) and do their homework.
And even if Amazon is tunneling all traffic now, that may change or someone may find a way to break out of it.
And even if law enforcement sees that the traffic is from Sidewalk, our legal system is pretty shit regarding the internet and I bet a dedicated prosecutor would try to get you for aiding a criminal because you technically allowed that access to your network. Look at the legal issues around running TOR exit nodes and the uncertainty there, in a lot of ways this is an opt-out version of that. (though I admit this might be a stretch, but I don't trust the legal system enough to handle this well).