Every time my group starts a new campaign or adventure with new characters, the caveat is that they must try and play something new and different. None of them have played a cleric, ever.
The Problem: Worship and Theism
I have tried to tempt the players into the Cleric role: amazing spell list, very versatile play styles, could be great fun roleplaying (basically built in to character creation)! No bites. They even know that they won't be heal bots, they can get creative!
I feel that the piety aspect is what is holding them all back. Organized religion is something that they seem too cower away from. This stems from the fact, or the apparent fact that, despite the option allowing Clerics to follow an "ideal" instead, the PHB and errata seems to still direct a Cleric to choose a deity (emphasis mine):
While the vast majority of clerics revere a specific deity, a small number dedicate themselves to a divine concept worthy of devotion—such as battle, death, justice, or knowledge—free of a deific abstraction. (Work with your GM if you prefer this path to selecting a specific deity.)
Which, to me, translates into a Cleric needing to pick a specific deity.
Clerics who follow a philosophy must select a patron deity among the philosophy’s associated religions (they gain no additional benefits from adherence to a philosophy). -Inner Sea World Guide
Even clerics, who must choose one deity as their patron above all others, sometimes offer such minor prayers to divinities allied with their chosen gods, although their faith must still remain primarily focused on their deity of choice, for even the good gods can be jealous. -Inner Sea Gods
A follower of a specific pantheon may take the Pantheistic Blessing feat to gain access to a spell-like ability tied thematically to his or her chosen pantheon. Note that single-class clerics gain their powers through allegiance to a single deity, and therefore cannot select this feat. -Faiths and Philosophies
And, while not a handbook, here is one of Creative Director James Jacobs' innumerable direct statements on the matter:
The official stance in Golarion is that if you're a cleric, you MUST have a patron deity. That's one of the big things that makes clerics not a different type of spellcaster.
(And yes, I wish I had a time machine so I could go back and fix the Core Rulebook so that it says that there in the Core Rulebook as well.)
You're free to say clerics don't need deities in games you run, just as you're free to say wizards don't need spellbooks or rogues don't need thieves' tools or whatever... but the baseline assumption for our campaign setting is that clerics must worship a deity.
So, having established that a deity-less Cleric isn't really viable in our play setting: How can I encourage the players to give the Cleric a try without DM intervening and allowing a deity-less Cleric? And further to that, how can I help them roleplay the cleric so that it is fun and engaging?
Eventually, I suppose, once all other options have been exhausted, I'll have an entire party of clerics! :)