as seen project from https://blog.exploiter.id/2019/06/why-dont-share-out-network-access-from-exploited-router/ that i think should be illegal, but in one case there several condition that might be legal to done:

• the most legal are owner has permitting you
  (moreover they ask you to patch it then allowing you to use them)
• the network are public already
• people being volunteer to share out their network
• crowdfunded network

i will guessing something the future will happened if this project would be done, like apps that automatically connecting you wherever it covered, by tracking you moving and gave a list of access point that can be joined, or even dedicated network that only privileged user should used.

so, how about that? it is great if happened! more user and more connection created, connected everywhere! but in one case, the most sensitive i would imagine are tracking, you might connected everywhere but don’t you realize if people actually intercept and bug the area (depends on network) how to prevent it? i think the most suitable reason are you already patch it but forgot to upgrade more security.