Actually that isn't a better analogy. It isn't useful at all in this context. In fact most analogies used to support theft of wifi (or any other phrase that makes people more comfortable) completely fail, because they quite simply describe "comparative" circumstances that really aren't analogous. That includes water/wifi, because water is a part of The Commons (commercialization aside) and wifi is not-- UNLESS it is specifically advertised as such (ie, municipal wifi). I'm sure a sufficient degree of hair-splitting can provide the appearance of robust counterargument, but in the end it's nothing more than rank rationalization in defiance of logic and law.

Bottom line:

-yes, people SHOULD lock their wifi unless they deliberately choose to share
-no, unlocked wifi is NOT de facto "there for the taking" unless consent, explicit or implicit, is provided.

That's it in a nutshell. Arguments to the contary tend to be founded on illogic borne of a desire to defend a generally untenable position.

EDIT: it's possible, based on what Benson just said, that I misinterpreted the application of mwiktowy's analogy. On further reflection it does appear he was actually agreeing with the "no foul, no harm" postings I made earlier. If so I humbly apologize to mwiktowy.