I get the feeling that you think that wifi somehow eliminates bandwidth limits; that somehow, the wifi signal only sends out signal, that you only receive...and that the number of computers receiving the signal can be limitless, without affecting the amount of available bandwidth per computer. If this was all true, then it would be quite different, and you could probably justify your theft.
Cutting in on a wifi signal is exactly like directly tapping a line, being that once you are on the signal, you are occupying a portion of the physical pipe that connects the computer to the internet, every time you send and receive signals.
In radio, the number of receivers can be limitless. It does not matter how many receivers are receiving the signal...the signal will always remain just as strong, as long as you are close to the source. This is true for the wifi itself, but it is not true for the physical pipe connection. Every extra computer on a connection sending and receiving signals further decreases the amount of available bandwidth that is supplied by the pipe.
Eh...I am apparently not explaining this very well, but...I don't think it matters how well I explain it. No matter what, you are going to continue to look for a way to justify your theft.
Expecting stuff for free, at the expense of others...kind of sounds like grab-ass Socialism to me.