There are several reasons I feel paladins fight amongst themselves on the forums over their vision of what the class should be, and I've attempted to categorize them below.
Part of the problem is that many paladins feel increasingly frustrated for reasons that can primarily be traced back to itemization issues. Retribution may be fun, but requires the right type of gear to perform well in groups and raids. Protection is definitely the unsung hero these days -- considering that there seems to be a tank shortage on many servers -- but when compared to warriors, most paladins have a harder time becoming uncrushable and have less health on average, mostly due to points being spent in the wrong areas on Paladin tanking gear.
Retribution requires large amounts of attack power, melee crit, melee hit and a smattering of spell damage to be effective -- but with a couple of exceptions, most of the gear designed for retribution paladins is better suited for a Shockadin (Healing/DPS hybrid). As a result, many aspiring retributers that are in the know pick up gear designed for warriors, while those that are less informed pick up the Shockadin gear. This leads to inferior DPS for the Paladin, who ends up feeding the stereotype that retribution paladins are worthless noobs.
Protection items have many of the stats that are needed for the tank on the go, but not always in significant quantities. Blizzard seems to insist on spending stat points on Mana/5 for tanking gear. While the initial theory behind this was sound (paladins can't hold aggro without mana, so they need something to help with mana regen), experience has shown that with Spiritual Attunement, Mana/5 is almost completely pointless -- more than enough mana is regenerated by receiving heals. Thus, many pieces of protection gear are rendered inferior when compared to gear designed for warriors.
Wrath of the Lich King & Death Knights
On top of all of this frustration, Blizzard announced at BlizzCon that in Wrath of the Lich King a new hero class would be introduced -- the Death Knight. This quickly led to much speculation and heated debate on the Paladin forums -- some Holy paladins cheered, thinking that this would finally rid them of the Retnoobs. Retribution paladins seemed upset that instead of getting the buffs they felt are sorely needed, Blizzard ignored them altogether to focus on Death Knights.
While I'm of the opinion that the Death Knight will offer a different play style, and should be looked at as an alternative instead of a successor to the Retribution Paladin, there's a good chance that many paladins will simply take steps to obtain one out of sheer frustration. The constant mocking and general feeling of being at the bottom of the food chain that retribution paladins endure will certainly help push them to this end unless steps are taken by Blizzard to address some of the issues. It does look like change is coming, though it's still a little way into the future. Surprisingly, I haven't seen many Protection paladins complain about death knights -- according to Blizzard, they'll be viable tanks, and could potentially force my tanking brethren back into a healing role.
Despite all this, the Paladin population seems to be thriving -- Horde paladins have become a common sight, we're reasonably well represented in arenas and battlegrounds, and still highly desired both as tanks and healers in instances and raids.
Parallels with lore
Perhaps it is fitting that there has been (and continues to be) so much strife and upheaval within the Paladin class -- from a lore perspective, no other class has endured such hardships. When Arthas fell from grace he killed Uther Lightbringer, effectively scattering The Order of the Silver Hand. Without a strong leader, the remaining members of the order went their separate ways - some went off to form the Scarlet Crusade, others split into smaller factions or faded into obscurity.
More recently, paladins have had to deal with the fact that Blood Elves have forcefully stolen the power of the Light, and now twist it to meet their own ends -- this very act flies in the face of everything paladins have stood for since their creation after the end of the first war.
Still, there seems to be light at the end of the tunnel -- there is compelling evidence that Tirion Fording, who many players will remember for his memorable quest chain in the Eastern Plaguelands, will rise and take his place as Highlord of the new Order of the Silver Hand in the next expansion. It would be nice to see the Paladin player base come together in a similar fashion, and remember that even with all the problems the class currently faces, we're still one of the most flexible classes around. Whether we're on the front line, protecting our allies from attack, or in the back, healing the wounds they receive, or even charging into the fight to provide buffs and smash our enemies, you can bet that if there's a battle, a Paladin will be there to help.
The future of the Paladin
Blizzard has stated that they will be addressing Paladin concerns in a future patch -- while this is nothing new (it seems that almost every patch there's rumored changes to the class), they seem to learn from previous mistakes, so it's possible that eventually the tweaking will yield positive results.
I would like to encourage everyone who plays a Paladin to be tolerant of your fellows. You may not agree with how they are specced, but try to acknowledge that everyone plays this game for fun, and what is considered fun differs from person to person. Instead of ridiculing that Retribution Paladin in spell damage gear, suggest ways in which he might improve his DPS. Instead of telling a Protection Paladin that if they wanted to tank they should've rolled a Warrior, try thinking about the advantages that prot paladins have over other tanks. Instead of complaining about how Illumination was nerfed and that all your healing gear with spell crit on it is now worthless, focus on how much you're envied for your efficiency and survivability by all those Holy priests out there.
In the meantime, brothers and sisters, stay strong, and keep swinging that light!