It's not random, Shar tells them who it is, also to Clerics of Shar destruction of life might seem like a good thing, after all a lot of them join because they have suffered and Shar elivates the pain, so they think world without life would be a better place.
In D&D evil isn't arbitrary, it part of you, you can detect it will spells, certain magic items will only respond to certain alignments.
These spells were actually changed to respond to particular beings, aka demond, devils, celestial, fey, undead etc. not alignments.
For me you action have no moral consequences it reduces roleplay value.
Actions having consequances and alignment are two completely seperate things. NPC should react accordingly to actions that you have done, but you don't need alignment for thta. The consequance that you seem to want is something shifting on your characters sheet.
