The Blast Infidel Feat is:
Currently, the mechanics of Blast Infidel only allow it to affect spells that cause direct damage damage with Negative Energy (though, that is somewhat contradicted by Slay Living being supported, which is foremost a Save-or-Die spell, with a secondary dmg).Blast Infidel
Type of Feat: Class Ability
Prerequisites: Hierophant 1
Specifics: The Hierophant now deals double the damage for any negative energy spells that he casts (inflict wounds series, death knell, harm, slay living and negative energy ray). This does not apply to Vampiric Feast or Spell-like abilities.
Use: Automatic
However, Negative Energy is defined as:
Negative Energy comes from a physical plane in the Cosmology. That Plane has traits.Negative energy was a type of energy originating on the Negative Energy Plane. It manifested as a black, crackling surge of power.[1] It was the antithesis of positive energy, being the "lifeforce" of undead creatures,[2] healing them while causing harm to the living.[1]
Necromancy is a school that focuses on manipulating Negative Energy of that Plane:
Spells such as the Inflict Wounds line are from the School of Necromancy spell list. So is Death Knell, Harm, Slay Living AND Negative Energy Ray.Necromancy is the school of magic whose spells manipulate the power of death, unlife, and the life force. Spells involving the undead make up a large portion of this school, including animate dead and finger of death.[1] Highly focused on the Negative Energy Plane, most spells from this school drain abilities.[citation needed] This school is the one most associated with lichdom, a process that allows the caster to live (or rather, exist) in an undead state indefinitely by securing their essence in a receptacle known as a phylactery.[citation needed] A wizard who specializes in the necromantic school is called a necromancer.[2]
So...why not the other Divine Necromancy spells get affect by Blast Infidel?
As in, for the Divine Caster: Energy Drain, Healing Sting, Horrid Wilting (Suffering Domain granted), Poison, Symbol of Pain, Undeath to Death, and...wait for it...Vampiric Feast!
If it looks like negative energy, smells like negative energy, is powered by negative energy and is from a Magic School of Negative Energy (Necromancy), is it not a negative energy spell? That a Hierophant can cast? And thus, would not Blast Infidel have an affect on all those spells??

Cheers.