Of the three roles in WoW, healers are the odd man out. While mages might call it damage and a warrior might call it threat, the fact is that DPSers and tanks both excel at hurting their opponents. One of my guildmates often refers to tanking as "just DPSing from the front." Healers, on the other hand, have nearly no offensive capabilities. The developers were nice enough to give every healer a cheap spell or two to spam to make us feel like we're contributing, but our DPS is abysmal. Healers, more than any other role, are pointless without a group to support.
Throughout the years, we've heard the legends of the shockadin -- the holy paladin build that doled out merciful healing and wrathful judgement in equal doses. While offensive builds for the holy tree have always been around, they've never been truly viable in any serious situation. I love the thought of Holy Shocking some hunter right off his high horse, but the numbers just don't add up.