[wmf]

I'd be curious to see how accessing an open wifi can be made illegal.

Using the magic words "expectation of privacy". If we assume that the general public is clueless about computers and thus many people expect that their open wi-fi is private (even though technically it isn't), then there's a problem. Also see the debate about thermal camera scanning of homes.

...my laptop wifi is going to ask permission to the open wifi...

But that's not what Google did; they were sniffing traffic without associating, so the APs had no opportunity to deny access.