From a RP point of view, it makes sense that neutrals should hesitate about killing goodie/neutral mobs.. Since neutrals are barred from player killing without RP reasons (gets you turned evil (*mutter*)). Which in turn is in line with treating NPC:s the same as PC:s (a principle which is firmly applied at times, and ignored at other times.)

On the flipside, if neutrals need a RP reason to kill non-evil / non-aggro sides, it would kind of lead to a merging of neutral and good alignments.. Since neutral roles usually lack have a natural resaon to kill most non-evil beings; thus it still boils down to "i kill these things because i need training/XP/EQ/whatever - killing from greed. evil."

It's complex.