Define casuals, define ruin and define WoW, through your own experience, which will bring a new set of questions.
Casuals- no doubt have changed the game and how it is played. However I would argue that even the most elitist of theory-crafters still enjoys exploiting the path of least resistance. Does getting more for less actually harm the overall quality of the game and experience? This relates to 'ruin.'
Ruin- do the changes we see in the game-play somehow break our traditional views of how the game should be played? Or similarly, just to coin the term, does "casual style" of game-play degrade the experience and fun of the game, for both others and themselves? This relates to the game as a whole.
WoW- what elements of the game have been put at risk? What specific goals, expectations and accomplishments, of the game, and formerly present, that are no longer being met? This relates back to how casual style has changed the game.
Given, Casual-style=more for less.
Okay, so does having more for less actually harm my willingness to play? No.
Do I value LFR and items associated to a casual nature more than my current game-play? No.
Therefore I am no longer getting more for less.
Therefore because the casual-style undermines the value obtained from the game, any accomplishment made outside of the casual style is inefficient and a virtual waste of time.
Does that ruin a game? No, it changes the game to where your active members of the community are embittered for being treated poorly.