Helldritch
Hero
This is where you are wrong.You are correct, all RP for a domain does not need to be the same. Because Domains are cleric subclasses.
No, he is not. Because Domains are cleric subclasses. A sect is a sect. I can pick one, and not have the other.
You are right Max, I can't win when you refuse to even read what I wrote and consider it and instead scream "YOU ARE WRONG, I AM RIGHT!" as loud as you can.
Domains are not really cleric subclasses. And yet they are. As strangely as this dichotomy sounds. Clerics have no subclasses per say. This is because this choice is extremely limited...
If clerics could really choose their "subclasses" You could see.
War Clerics of Eldath (Peace and Serenity). (though it might be fun to see an Ethos like that. WE WILL BRING YOU PEACE! WHETER YOU WANT IT OR NOT!)
Death Clerics of Pelor! (If life lets you down, undeath will bring you back up!)
Trickster Clerics of Torm, Tyr and Helm! (We will trick you into following the law...)
Life Clerics of Nerul. (With us, you can die any time. We will bring you back for more...)
and so on.
The clerics domains are subclasses in the sense that you can only pick the one(s) that your deity allows you to pick. Compared to all other classes this is a HUGE restriction. It must then mean something more than just a subclass. Some RP must derive from this. After all, Paladins are now free of the Gods and as a "usually religious" class, they can have access to all their subclasses no matter which deity they worship. It can be perfectly possible to have an "avenger" of Eldath.
So yes, whether you want it or not, domains are also a focus on which aspect of your deity you worship. These can then be put into different churches worshipping different aspect of the deity. This is why in the Acolyte background you have to (and not should or might) consider the domain of worship you will take. Only the cleric derives power from that choice. But to all others, it is a choice nonetheless and this choice has more meaning than what you want it to have.
On good deities, this probably won't bring a lot dissension between the practioners. But in Evil religions, this can lead to unholy wars quite fast. You wanted to know the use of evil deities? You have one right here. How? Simple.
Acolytes and cultists can be non casters, so they do not communicate with their deity (in fact, cleric do not communicate either until mid to high level). But their acolytes must choose a domain/sect. This can lead to bad or misguided interpretations. Which might leads to wars and ruthless combats between two sects (or more).