I have told players to quit. I've told several on these very forums. I tell them that when they express not finding any enjoyment playing the game. If you're bored to tears, constantly complaining, and want the game to change to fit your particular playstyle, I am going to tell you to find another game to play. Simple as that.

In terms of someone who plays so much that it is negatively impacting their real life, I won't tell them to quit. I will however tell them to get out of the house for at least a few hours, and whatever they have going on in the game can wait. If you have a raiding schedule, then redo it. Get the hell out of the house!

I don't know how I would react if someone told me to quit. It would be heartbreaking to come from someone I care about who knows how much I love playing this game and my attachment to my character. From some rando, I couldn't care less what they tell me or think of me, and I would tell them sit on the fist that should be in their mouth. Either way, the reaction wouldn't be good and I'm glad everyone smarter than a troll would never say this to me.