I would argue that inductive coupling from overhead lines is not theft. If it is, then the electromagnetic radiation is trespassing on my property. If somebody doesn't want me to utilize something that's in the air, keep it off of my property. I apply the same logic to radio waves, if someone doesn't want me receiving them and listening, don't transmit them near me.
You can make that argument, and I am reasonably sure somebody has, but it will come down to them being a public utility and your rights are out the window. Think 'eminent domain'... Sure, only a government agency can invoke it but they can turn it over to whomever they wish - like a public utility.
From experience, I can tell you that you don't want to lay wire on the ground under a 115 kV bus works. No, I didn't get hammered but I could see the effect with a non-contact voltage detector.
I don't think inductive coupling will be effective at low residential voltages but I can't say I ever tried it.
I once had a gas fired hot tub and it could do some serious damage to the utility bill.