Adding onto this thought, even if life can arise under extreme conditions, the probability of necessary events could still be far lower than the probability of necessary events for life to arise under earth-like conditions.
Thus, the habitable zone criteria is simply narrowing the search space to planets with a high(er) probability of developing and supporting life--while discarding planets with a low(er) probability (though some discarded may indeed have life). It seems reasonable to me in this light, as well.
there is probably more chance of finding intelligent life on planet that is not habitable and can't originate life. because once life becomes "intelligent" it will probably try to colonize more than one "uninhabitable" planet by intelligent machines designed for specific environment.
Thus, the habitable zone criteria is simply narrowing the search space to planets with a high(er) probability of developing and supporting life--while discarding planets with a low(er) probability (though some discarded may indeed have life). It seems reasonable to me in this light, as well.