One of the interesting points to navigate when you deal with the issue of “monsters” in the vaguest sense is that there’s a core idea that defines how the audience (and in tabletop RPGs, the people playing) should consider them.
“Monster” in the sense of a terrible evil. It cannot be truly reasoned with or change of it’s own accord. The stuff of myth and legend. Surviving encountering it is victory, killing/destroying/trapping it is miraculous, and bargaining or trying to co-exist is folly. Many horror movie monsters/killers are this sort of thing, and they fill the same role as old folklore monsters.*
Beasts are like animals – they may be harmful, as much as a hungry tiger is harmful, but they are not evil, nor capable of making a moral choice in any direction. On one end of the scale, they might be a danger that can be kept at a distance and people could live with, on the other end of the scale they are too invasive/harmful to endure – the xenomorphs from Aliens, for example.
These are “Monsters” might be what the things look like, what they can do, or they may need to survive on blood or dead flesh or fear, or something similar, but they’re actually fully cognizant and capable of making moral decisions as much as anyone else.
Importance for creators
Think of these 3 categories, and you can probably think of movies or stories with classic monsters where they have filled these different roles depending on the way the story wanted to treat them – vampires, werewolves, ghosts, orcs, aliens, demons, Lucifer as a character, etc.
While there’s certainly a good number of stories around people mistaking categories – either as a note about bigotry (mistaking People for anything else) or horrific naivete (mistaking anything else for People), when you are the person creating the events in play – as a GM and as players, you don’t want to be mixed up about it.
The general trend in stories in the last 20 years has been to make more of the classic monsters into the People category, so it’s not new, although it has shifted the landscape drastically. The stories you tell about people surviving EVIL vs. people dealing with dangerous nature are NOT the same as people dealing with other people.
I think this is one of the reasons we’ve seen more stories about zombies -these stories still accept the monsters as either capital M-Monsters or beasts operating on some kind of instinct and not conscious choice. Although you can find stories where these are considered people, for the most part the expectation is that they are NOT people, and the issues in dealing with them and the entertainment value of fictional violence can be had without guilt.**
The Troubling Space of Stand-ins
Creatures in all three categories have long been stand-ins for human interactions throughout history, though it’s a fraught area to navigate.
For example, the vampire-as-abuser dynamic is a common one, though with good consideration it can be a great critical look at abusers. On the other hand, you have stuff like “orcs” where the descriptions of orcs turns out to be lifted nearly word for word with the terminology used to justify colonialism and genocide in the real world. So… then the stand-in factor is basically an expression of real world racism transposed to an “acceptable” target.
This becomes even more pronounced when the given story/fictional world is absent said people as well – “Group X doesn’t exist in this world, just the Horrific Monster People who have all these traits that neonazis and white supremacists attribute to Group X…”
So… you end up with this rather twisted space of “I’ll create a fictional creature group as People and then ‘un-People’ them using the exact same logic folks use in the real world against real people… for FUN!” (the even thinner version of this is to create stand-in fictional humans and declare that in this fictional world, these walking stereotypes ARE “like that” and therefore, it “isn’t racist”.)
What’s this mean for your game?
If the game revolves around playing, or interacting with a given creature set, it’s good to set the expectations of what category things fall into, or that you’ll be playing.
Vampires as People vs. Vampires that are People that can devolve into Monsters vs. Vampires as Monsters are three very different kinds of stories to play in.
Games that have a lot of different types of creatures may have all three categories covered, in which case, you have a different problem about considering when/where/why some get some treatment and others get a different treatment despite being more-or-less the same.
The classic problems of D&D’s “evil alignment races” has always been along this line. My usual cop out is to redefine such things and either firmly put creatures into the People category, or make them some kind of creation of magic where they are Monsters or Beasts – not sentient folks who have kids and hopes and dreams, etc. It still means a bit of work both on the backend of creating it and explaining to players.
This is one of those things any pre-existing setting should have already handled and made clear, but for many games and settings, it’s a nebulous or unclear thing, often the result of a mishmash of many people creating a setting without much consultation or consideration of overarching narrative themes or real world biases.
And of course, in the classic tabletop RPG fashion, it’s left to us at the table to fix what shouldn’t have been absent/broken in the first place.
* There’s occasional stories of the horror movie monster finding redemption or being released from their role of evil, however that happens primarily through the actions of protagonists, and not the agency of the monster itself. The monster will not change without someone else forcing it to change.
**Zombie stories complicate this a little by questioning the time of when someone “turns”, but you don’t see people turn BACK after they become zombies. And of course, the whole zombie mythos being used that way is EXTRA fucked up in regard to “guilt free violence” when you consider it’s original mythology of the horror of dehumanization and eternal slavery…