(Reposted because I forgot to log in)
The problem with your first statement is that having a "good and valid reasons for leaving a wifi network unpassworded" doesn't mean that those reasons afford you an expectation of privacy, and so, is irrelevant to the discussion.
As to Google's sniffing being more intrusive than a reasonable person would expect, there is no need for the metaphorical telescope. This situation is more akin to going around your neighborhood, telling everyone that they are free to use your windows and doors, and then acting surprised when someone sees you in the shower. The people who are utilizing open WiFi are sending out beacons saying "I'm here, I'm unencrypted, feel free to use me."
Keep in mind, the WiFi Alliance has mandated that Access Point ship with encryption enabled by default for something like a decade, which is longer than the expected lifespan of most wireless gear. The vast majority of people utilizing Open networks have, at some point, made a choice to have their network be unencrypted and accessible by anyone who cares to join.