Okay, so I'm the longest standing TF druid (/patsbackandlookssmug) so I think perhaps I should say something about this.
First off, ground rule: Wife > WoW. If she's not cool with you playing a druid, and your arguments don't sway her, you're best off playing one of the less awesome classes.
Secondly, when I started playing my druid, I had to think about this sort of thing too. I had just got out of a rather dark time of my life, spiritual attack, that sort of thing. I wasn't sure I wanted to get involved with something that would harm my walk with God.
When it comes down to it, it's a personal question of your involvement in the game and your ability to separate the realities from the pseudorealities. Let me explain: When I play Neirai, my druid, I am fundamentally (in reality) playing the most hybrid class in a game, with certain rules that apply uniquely to me and not to other, more pure classes.
When I "cast spells," I am simply pressing certain keys that have certain effects on the game.
When I "complete quests," I am simply completing certain challenges in the game.
When I "kill monsters," I am simply interacting with certain challenging elements in the game.
When I "hang out with friends," I am simply hanging out with my friends.
When broken down in this manner, one can see that WoW isn't so different than snakes & ladders or cribbage, or Super Mario World. It's just oh-so-much more complex. More rules, more elements, more people.
Part of making WoW fun and not totally way too complex is the "flavor" attached to the game. This is simply because nobody really wants to choose between the following classes:
Standbackandshootthingsguythatdiesfast
Standbackandshootthingsguythatdiesfastbuthasachoiceofpets
Standbackandshootthingsguythathassneakymovesandonlyonepet
Standbackandhealthingsguythatdiesfast
Getinthewayofthingsguythatneedstobehealed
Guywithsneakymovesandalotofmeleedamage
Standbackandhealguywhohaslotsofarmorandcangetinthewayofthings
Killthingsalotguywhocanimprovepartydamage
Guythatcandoalloftheabovebutonlyoneatatime
As you can see, that's not only boring, it's hard to read! So Blizzard chose to use thematic elements to make the game more interesting. One of the themes they chose is religion. Paladins (Monistic Spiritualism), Night Elves (Nature worship), Orcs/Taurens/Shamans (Animal/Elemental Spirit Worship), Trolls (Voodoo), Blood Elves (themselves), Dwarves (the Makers), etc.
So what I'm saying is, it depends on whether or not you can separate the reality (I click buttons to accomplish tasks to complete challenges) from the pseudoreality (I just mercilessly massacred a town of innocent murlocs just so that I could get a new hat.) Or, more specifically, I play a hybrid class with the ability to fill any role, just only one at a time; or, I worship trees and sacrifice virgins to maypoles.
I would strongly council you that if you (or your wife) cannot make the break between reality and pseudoreality, you don't play the druid.
I hope this helps. I know my thoughts are a bit scattered.
P.S. Yes, I know I'm the greatest campaigner for WoW is reality, but that a subject for a different time. That's why I call it pseudoreality, and not "fake" "a game" or "fiction."