I can't believe 13 people answered "depends"!
Look, I agree with you that no one "owns" the radio waves. But if I'm paying $50.00 per month for X Kbps downstream and Y Kbps upstream, I better fucking get all X Kbps downstream and all Y Kbps upstream at all times!
Yes, you are right...the radio waves from my wifi antenna to my computer is not able to be owned, but the portion of the pipe that connects me to the internet is certainly able to be owned.
Now, if you found someway to "steal" an internet connection such that NO ONE ELSE's connection would be interfered with AT ALL (which would be basically impossible, unless you build your own pipes...which would give you ownership of those pipes)...then, perhapse I'd have no qualms. But until then, you are stealing property.
I see how this debate is getting confused with the "radio waves" debate...but the two are not the same. Radio waves depend on a medium that cannot be owned...i.e., air. But the internet depends on a medium that certainly can be and is owned...i.e., pipes.
In radio...if you can afford to buy a machine that broadcasts and recieves radio signals, then you should have all the right to do so. But, if you poke a little hole in my internet pipe and leech off it...you are stealing my bandwidth, and you just simply do not have a right to do that. It's freaking theft!