Both. Justice is something that everyone should deserves, and it should be enforced at times, no exceptions. You have a law, follow it. No one should be lawbreakers slide. But mercy is equally important, because there is time when one has to know when it's okay to not slam someone behind bars, electrocute them, take their kids away. Mercy should be exercised when it is deserved. When you have you desperate woman steal bread from a store to feed her now starving and almost malnutritioned kids because their lives got destroyed by a hurricane. The last thing people should be thinking of doing is locking her behind bars and taking her kids away. Over some damn bread?! Some bread?! Um no. Especially when you have rich heirs of millions getting away with raping their children! That's some straight up bullshit.
Justice is easily corrupt. There's in no real way real justice. It's all in the eye of the beholder or law makers as to what justice really is. There's never any real rhyme or reason for why we have our laws. Give me a logical reason that I see as logical to why someone smuggling a ton of pot gets more time then a child rapist and I'll officially spew how amazing you are all over the Internet. There's never any just law since laws change constant and sporadically to support issuing control over the people. We treat people in prison or celebrities better then we treat the people who have been maimed in America who have fought for the supposed laws that keep our system "just". Is our system just? No not in the slightest. But there's never any tried and true just law system. There can't be. If you impose laws in a way you're going to have to disregard the few who will be hurt by those laws and the system for the many. That's what justice technically is and all it is. Justice doesn't really show mercy. Mercy however is not the way of cowards it's the way of people who choose to have the human experience of altruism and compassion. It's apart of what makes us human. Why would the only human experience be deemed cowardly?
Eye for an eye, hand for a hand is my motto. So I guess justice. It may make the world blind but at least then we wouldn't be able to see and fuck more shit up. And maybe if there wasn't so many awful people in the world an eye for an eye wouldn't make the world blind. Some people don't deserve mercy (such as pedophiles, rapists and murders) no matter their age, race, etc. mercy for those people isn't justice for the ones who's lives they have ruined and that is wrong.
^ you do realize that not all pedophiles act out on their urges some seek help right away and a wide range of pedophiles were they themselves sexually abused as children?