Rather than BAD analogies, let me use a very DIRECTLY pertinent one. Suppose your neighbor has a cordless phone. You go to a garage sale and buy the same phone. Now you use it to make calls on THEIR phone line.
At this point you have crossed the line from simply “reading using their porchlight” to actively sending signal into their house attempting to use their utility.
If you can’t see where this is active and knowledgeable intrusion, and unethical and probably illegal, I can’t help you with that. State and Federal laws take a dim view however of intruding onto computer networks. Beware.
Personally in past I have paid neighbors to share their service. At the moment I am doing the sharing, my ISP is Sonic.net which allows and encourages it. I maintain the connection, the girls next door kick in $20/month for all 3 of them, everybody is happy and EVERYONE AGREED ON IT. Don’t want to turn this discussion off in the wrong direction but just had to say something REAL instead of the ridiculously chosen analogies I often see trotted out.