I dont think it is.
I think you clean up Volo's, and either we leave the rest alone as it pertains to setting specific definitions (FR Orcs != Eberron Orcs) or we have another layer of errata that sapient beings are not of a predefined monolithic alignment.
That's not a slippery slope, it's 'apply a patch to alignment'. IMO of course.
I misread what you initially wrote. Mea culpa.