Oh yawn, here we go again. Print this out on a little card and keep it with you.
1 - accessing WiFi without permission is in many countries illegal, IRRESPECTIVE of the WiFi being encrypted or not. It's the equivalent of walking into a house because the door was left unlocked, that is stupid, but it still doesn't legalise you gaining access to the network (even if some products do this now automatically). Here is an example of a conviction in the US.
But let's assume, for a minute, that it was OK to access an open WiFi without permission. There is another problem: data privacy.
2 - Google is a business, and a business has to comply with laws. The moment there is a mere POTENTIAL of acquiring personal information, permission has to be gained from the individual involved. Given that Google could potentially acquire information deemed "sensitive" under EU law, it would have to gain EXPLICIT permission. Even for US companies, "you let me drive past your house" is not considered enough as a permission statement.
In the US they're a bit more relaxed about it (hence the pityful fines), but the EU has actually been too friendly here, and the lobbying proves that Google jolly well knows it got away with breaking the law once, and is worried about not being to pull that off a second time.