Most creatures tainted by Chaos are simply evil. They tend to worship the gods of Chaos – the enemies of Creation – because no one else will take them. These entities are opposed by the gods, who uphold the cosmos as part of the Great Compromise. This isn’t just a Theyalan thing – no God Time deity untainted by Chaos is better than neutral towards Chaos; most are hostile or enemies. They have their stories as to why they are what they are, but in the end this is not a “misunderstanding” by the gods – beings such as Krarsht, Thanatar, Thed, Vivamort, etc. are evil..
The very life-cycles of many Chaotic creatures are corrupted in ways that most sentient beings find far more terrifying than mere man-eating trolls or alien dragonewts. For example:
Broos are like vile fast-breeding parasitic wasps and propagate their species through the violent implantation of parasitic larvae into living hosts. They are immune to disease but serve as carriers and spreaders like mosquitos.
Scorpion men survive by having their queens devour living sentients and then performing the ritual of rebirth where that sentient being is reborn as scorpion man – possessing their former intelligence but usually completely mad from the horrible experience.
Ogres are the ultimate racial supremacists, literally feeding on those peoples they consider inferior (in other words all non-ogres).
These life-cycles are locked in Time as a result of God Time events, just as all mortals need to die because of the death of Grandfather Mortal.
Important cults such as Storm Bull, Orlanth, Ernalda, Kyger Litor, and Magasta are utterly opposed to Chaos – indeed the very raison détre of Storm Bull is to seek Chaos and destroy it. I do not begrudge any player characters whose only reaction to encountering Chaotic creatures is to kill it or flee from it.
And yet, there are those that claim that it need not always be like that. Nysalor taught that through Illumination our inherent fear of Chaos can be overcome – and also that the inherent hatred Chaotic beings have for existence can also be overcome. This is at the very core of the Red Goddess cult and is integral to the Lunar Way.
There are also stories of Chaotic creatures rejecting the Lords of Terror and seeking peaceful coexistence with the rest of the world. The fabled Cleansed Broo of the Rockwood Mountains, who devoted itself to Chalana Arroy is perhaps the best known, but there are of course others.
And thus even those tainted by Chaos have a possible depth, motivation, and the chance to be more than they are.
As an aside, I do not consider ANY of the Chaotic cults appropriate for player characters, with one very exception – Nysalor/Red Goddess.
Beginning players are often tempted to play an evil character. I personally found it boring and much less rewarding. I strongly agree with you. Which is why in my opinion playing a Chaotic cultist (except for Nysalor/Red Goddess) is not something we encourage or support. Any more than we support playing a cultist in Call of Cthulhu.