Remathilis
Legend
Hold up.Any intelligent, self-willed being has the potential for complexity, even mind flayers. If you want an enemy you can turn your moral compass off for you have things like mindless undead, constructs, oozes, etc.
I'm absolutely willing to accept humanoids have free will, but I'm not as ready to accept that most other monsters need be so complicated. aberrations and fey have very alien minds and notions of good and evil. Fiends, elementals and celestials are made of raw (aligned) planar energy. Unread are tied to negative energy that warps their minds l. Many types of monstrosities are likewise either bestial or have a different mindset to humanoids. The only ones I might give some leeway on are giants and dragons, and even then they have such a thematic connection to elemental heritage and deities that I'm willing to "usually" an alignment.
That's not to say such a creature can't fight their instincts and be a different alignment. That though should be rare and memorable. I also love Eberron, but I think that making alignment overly fluid removes some of the noir feel of the setting. The biggest thing I don't want though is losing the ability to fight monsters without going through due process. I don't mind losing orc hordes, but I want to keep some monster on the ok to fight list. Let exceptions like Falls-From-Grace or Large Luigi be exceptional while the mind flayer ship that just took orbit over Daggerdale probably isn't looking to establish trade relations.