I think this is a perfect quote that illustrates why some groups feel the "need" for roles.
In my view however explicit roles that are used to tell players how to act have no use in D&D. The negative energy cleric is having fun playin a role in his head and the system is letting him, that is awesome. Another player could play a Paladin and we could roleplay the tension that might occur with that. Or the party can purchase some healing potions, or seek out some wands of healing, or they can choose to seek lower level challenges. Or the DM can modify encounters, or supply the appropriate magic items to help alleviate the problem, or an NPC could pop in now and then. Maybe the next adventure the party encounters a troubled magical creature in the woods and if they save them, a druid in the woods offers free healing every time they visit the grove (but perhaps not to the one who radiates negative energy).
There are plenty of solutions to this "problem" (which really isn't a problem because playing your character the way you want is the very nature of the game). The least acceptable solution to me would be forcing classes into specific roles.
I think this illustrates the different types of D&D people play. I have played in games where the DM shows the purchased module and says to the players "lets see if you guys can beat the module". These games usually devolve into tactile mini wargames with much less roleplaying and I can see the need for strict roles in this type of D&D. I have also been in games where DMs use modules as guidance and form their world according to the players choices (if a player chooses a barbarian they meet his tribe, if a player roleplays a warlock their sure to include some witching sites in the world, if no one in the group chooses a healer, the DM reacts to that too). I much prefer games with an active DM who doesn't blame things on the rules. I have DM'd an all Paladin party, and all gnome party, and parties with no magic users, I do not believe it should be too onerous to run a fun game with no healers in Pathfinder.
quoted because I can't XP it twice.
We need to be able to choose, not be limited by the system. If we want a "useless" party;
Bard (playing as sage-like thief)
Quarter Staff Fighter
Wizard (Alchemist)
Rapier Fighter (displaced nobleman)
then we should have the option and the DM and players adapt. Forcing a particular class to be good at a role is no good no good.
Players of other styles/opinions can develop their group as they see fit*
Fighter (Longsword/Shield)
Cleric of Fire and Holy Flame (oww it hurts when you heal us!!)
Sneaky Rogue
Wizard (Storms and Enchantments)
It's all good.
*both actual play groups in my campaigns