Compare the way Harm is written to this way:Harm charges a subject with negative energy that deals 10 points of damage per caster level (to a maximum of 150 points at 15th level), but it cannot reduce the target’s hit points to less than 1. If the creature successfully saves, harm deals half this amount.
If the clause about the 1 HP was in the first sentence as in my 'rewrite', I'd agree with you. That 1 HP clause is in the sentence that talks about the save, though. So, unless the target saves, it can go below 1 HP. I don't really see any other way to read it.
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