There has been no greater fictional contrast of brothers morally than that of the Uchihas.

Warning!! If you watch Naruto this is a spoiler so don't blame me for not warning. I request that there is a level of trust not usually permitted in debates in that I don't have to source what I say and we shall assumed this is really the storyline. I shall give same trust to you. Now as stated in round one, this will be my opening speech. Itachi was Sasuke's older brother, and older by quite an age gap... Though this is never stated directly in the Anime as far as I remember. I'd estimate it to be as large as 7 if you see their physical appearances change in Shippuden it's obvious that Itachi is in his mid twenties whilst Sasuke is only about 16-17 (Naruto Shippuden is basically like a time lapse after Naruto, he has basically hit puberty in Shippuden whereas he was a kid beforehand... As was Sasuke). Itachi always outshines Sasuke and their father, Fugaku, always had a HUGE favouritism for Itachi, never praising Sasuke only saying that at Sasuke's age Itachi was much more skilled than him (Itachi is just one of those kid ninja whose good at everything whilst Sasuke was only really good at Melee fighting to begin with). So anyway... One day Itachi was faced with a dilemma that, had Sasuke been faced with, he definitely would have picked the opposite and hence spends his whole life seeking to avenge Itachi for the choice he made, and then when having killed Itachi and realising the true selflessness of his brother, he is infuriated at the people who forced his brother to choose such a horrific decision and then, ironically fights for the very cause Itachi died for (at Sasuke's hands). The dilemma Itachi was faced with was this... I'm sure even a non Naruto-fan can drop their jaw at how hard a choice it was to make. He was about 17-18. He was a member of the Leaf Village's (the leaf village is the village in which almost all the Uchihas lived) secret agent force named ANBU (equivalent of CIA to USA). He was also, however, a highly trusted member of the Uchiha clan's inner circle (of which his Fugaku, his father, was the head). Now being an Uchiha in the leaf village had, for decades, seemed to have been analogous to being an atheist in congress. You just stood no chance politically. For years the Uzumacki clan had ruled the leaf village since long a go an all out brawl between the clans had ended up 'proving' the Uzumacki clan to be better and the contract agreement said whoever wins is proof that their clan is the superior one... The thing was that that particular Uzumacki member happened to have wood element chakra that is basically a weird form of chakra energy that is extremely hard for even the strongest ninja to defend. So Itachi's Father declared that in a week the Uchiha clan would definitely raid the entire town to overthrow the Hokage (equivalent to ninja president of leaf village) and regain Uchiha status in the village. This Coup D'Etat startled Itachi because he had been trained, as an ANBU agent to immediately notify the Hokage and his inner circle of ANY threat regardless of how close her was personally to the person being reported... So, Itachi being Itachi... He naively reported it but only the DAY before the planned Coup D'Etat. So the Hokage, in his fury left Itachi with two options. To either kill the entire population of the Uchiha clan in leaf village (the few lost Uchihas elsewhere were irrelevant) or to let them survive and watch the leaf village be destroyed. You see if the Uchihas were to successfully carry out the Coup D'Etat then they would overthrow the entire political leaders and the Fire village, who happened to have a huge grudge against the leaf village and, unlike the leaf village, was all one big family, would invade and inevitably the Uchiha clan would have ended up thwarted regardless of their temporary gaining of power. The reason Itachi was so strong and able to kill his clan was largely due to a unique eye he'd developed by killing his best friend (there are two ways to get this eye-power, it's called Mangekyou Sharingan and is either got by killing your best friend or a relative dying in your arms while possessing it, which is how Itachi eventually passed it onto Sasuke. You see he waited for a long time until Sasuke was out of town and safely at school and then began his rampage but he had overestimated himself. Whilst he had the huge advantage of absolutely no one expecting him to attack since he was their family, he had the disadvantage that all Uchihas posses a Sharingan eye and that what Sharingan does is offer an extreme edge in seeing your opponents movements. The Mangekyou Sharingan enables one to create illusions in their opponent's mind and hence makes fighting them ridiculously easy as they can't sense you at all and are instead fighting an imaginary you in a parallel universe that you created in their mind. Nonetheless the Uchihas are very strong people and he seemed to be unable to hold them off long enough to finish off before the children returned form school... then he had no choice because the mission order said to kill ALL Uchihas but he had hoped that if he'd killed the adults it would be okay... he was in such a emotional state of fury that he slaughtered babies elderlies and children left right and centre and he had left his family for last. He killed his, and Sasuke's, parents but then Sasuke (only a little 8 year old at the time) walked in to the most traumatising site of his life. His big brother stood over the two dead bodies of his parents. Now while Sasuke hated his father, just as Itachi had been his father's favourite, Sasuke had been his mother's and something in him snapped when he saw her and started screaming and punching Itachi who just couldn't bring himself to kill his little brother. Then the Homage said he'd allow Sasuke to live as a village orphan if Itachi would leave the village join the Akatsuki (a highly group of skilled ninja forming the most notorious criminal gang of Naruto) to spy on them and to never EVER tell his brother or ANYONE he knew the true reason he killed his family. To never EVER dare be claimed a hero and to die with the reputation of a villain. He said that if Itachi were to ever dare reveal the truth to Sasuke, or anyone for that matter, He would order ANBU to kill Sasuke in the blink of an eye. Itachi loved his little brother too much and ended up dying in his arms. However due to the fact that there was no way Sasuke could have known the truth especially considering how brutally he lived to get revenge on his brother. However Sasuke vowed to never get it by Mangekyou sharingan but to find his own path in life o kill Itachi. He REALLY DID Join a criminal gang named The Hebi led by a man named Orochimaru who gave Sasuke a demonic power that converts your sanity into physical prowess but hurts like hell to use. Unfortunately, when Sasuke does kill Itachi, having already killed Orochimaru, and learns the truth of the story he vows to destroy the leaf village an "Let everyone know his pain" Whereas Itachi had always said "You will know my hate one day Sasuke" Sasuke always says "You will know my pain one day when he is having an emotionally significant battle with someone. Itachi is the pinnacle of Utilitarianism whilst Sasuke is the pinnacle of Moral nihilism. He has only morals driven first by vengeance, then by pure sadism...