But it would have broken out into civil war eventually and maybe into shinobi world war considering the immense powers Sharingan gives you, maybe some other village like mist would have tried to help Uchiha(don't forget Mizukage was under control of Obito).
I agree war/violence is never justifiable, but one has to go for war by concealing his feeling. It isn't easy to go for war or do massacre, even Itachi cried like a baby when he had to kill his parents. Wars/Massacre don't happen everyday, but when they happen both sides have to face the consequences, but isn't completely possible to 'avoid' them.
Talking about Pandawas, yes they finally suffered through the mental consequences, but that doesn't mean what they did was 'wrong'. They had to do it, because war is unavoidable sometimes and one has to fight for better future. In Hindu religon, even gods had to participate in the wars, even in Gita it is said that,
'Considering your specific duty as a kṣatriya, you should know that there is no better engagement for you than fighting on religious principles; and so there is no need for hesitation.'
So war isn't solution, but it is unavoidable.