Edit- Ryios said it better than I did. So you can skip this text bubble. I should read more posts before giving up on the replies.

Think of it like this. This is a game. You play to enjoy it.

Now consider that being an MMO you are going to play with others. It is much more like a team sport. Your actions, performance, attitude and so on directly effect the rest of your group. So while you enjoy the game it isn't about you or any of them. It is about the group working to achieve the goal (kill the thing, usually efficiently and with few / 0 retries).

When people say 'this is only a game' or compare it to something single player they seem to forget how connected they are to the experience of those in the party with them. This isn't Mario. This isn't FF XIII.

None of this justifies people being dbags about experience. However being on the opposite extreme is no better.