She reminds this hapless soul that "the law is the law" and has him publicly executed. The crowd of slaves starts hissing, and she gets this pinched look in her face which is essentially what I think she might look like if passing a kidney stone. I've seen this look a lot lately (sometimes at my own work) as management struggles to come to terms with the budget deficit in our agency and liquidates positions. There's that "pinched" look in the face. Are you passing a kidney stone? No? Oh, I recognize that look...you are trying to be "fair."
But here's the thing people. Our idea of fairness isn't actually obtainable. In fact, it's probably the greatest lie ever spread by humans because it's a cloak for wishful thinking. If life was actually fair, companies would only fail if everyone who worked for them was evil and raindrops would fall only on bad people. So essentially we all have a broken idea of fairness. Our idea of fairness always serves "self interest." Oh your opinion coincides with mine? That's fair. Oh it doesn't? I cry foul. People love to invent moral authority and buy into the whole concept that if you work hard you will succeed. But there's plenty of situations where this is simply not true. The only ones you hear about though are the ones that do succeed. So the lie perpetuates itself.
In real life, children would be better served if they were told that life is a competition instead of telling them that it isn't. "Remember kids, life isn't a competition. I mean apart from grades, jobs, colleges, partners, wealth, and status. Yup...no competition so just do your best." And that's my epiphany about Daenerys' situation in Merene. I mean, maybe that's what the game of thrones is actually about. Cersei says, "To play the game of thrones you either win or you die." Well, no, but that does make a good sound bite. If Daenerys knows what's good for her, she'll embrace a different philosophy: to play the game of thrones means to realize that life isn't fair. Therefore you shouldn't strive to be a fair ruler, just a good one. You shouldn't have killed the slave. Sure, it wouldn't have been fair, but who cares? Life is a competition and you've got to play your advantages. That's just the nature of reality. Everyone who doesn't admit that (whether in George R.R. Martin's fantasy world or the real one that we all live in) is in denial. But I suppose that most of us get hung up on how we think the world should work that we fail to see how it actually does work.