And not only will I force him to write MM and all the characters I like, but I will also take in hostage his family, his pets, all his friends (even the Facebook ones) his car and his X-Box if necessary..What the hell do you think I'm doing here ? Do you think I'm here for kidding ?
Fanatism apart, I'd refer to what I already said : it depends if you're a writer or not.
One of the first thing you learn in writing-class (and/or story-telling class) is to appropriating your self every kind of constraint, because the first story you will have to write for hire isn't especially the one you would wish. But isn't everything in life a matter of choices, eh ?