Actually trespassing on private property might be a better analogy (obviously it's not equivalent to "breaking and entering" if there's nothing to break). If you needed to step onto someone's private property for a trivial purpose such as retrieving a ball, or just stopping to tie your shoelace, that might technically be trespassing, but obviously not a major concern unless it was repeated abuse. Perhaps unprotected WiFi access could be considered in a similar way. If you access a unprotected WiFi link momentarily to check your email without knowing exactly where it's coming from, that's a trivial trespass that isn't doing any harm to anyone. If you did it all day every day using your neighbour's WiFi instead of getting your own internet access, that might be worth getting annoyed about. If you were using it download massive amounts of warez and porn, that would certainly be criminal trespass.