The issue of free wifi usage indeed is a slippery slope that we can argue for ages and never get a real answer. If the law says its illegal, then the person in question will probably get in trouble for it if caught and prosecuted. But that does not mean that in the court of law, the person will be found guilty. A good lawyer can probably find reasonable doubt with the fictional scenario below:

If my neighbor does not want me to use his open wifi connection, then he needs to restrict his wifi coverage to be within the confines of his property.
If it extends to my property, then it becomes mine.

If he wants to charge or sue me for it, then I will have to sue him for listening to (enjoying) my stereo and tv when I bring them outside in my yard, as I paid for the electricity and the hardware. I may even charge him for breathing the air that my purifier has processed prior to it being blown over to nostrils in his front yard.

I will also charge him for trespassing my property with his Wifi Ghz waves