If anyone should of went all emo and dark it would be Itachi..
Seriously Sasuke is just...dumb, Itachi killed his whole clan, people he knew...starting with Shisui...all for the sake of peace in the village..he killed them all with his own hands (Shisui could be an exception, don't think Itachi was the one who killed him, Shisui gave his eye to Itachi before entering a battle he could not win) but his own family..slaughtered..did he go all batshit crazy and mentally unstable? no..he was cool calm and collected, even working in akatsuki he never showed any emotion for what he was forced to do for the sake of the village..
Yes Sasuke was setup for a twisted life..but hes the one who chose to destroy Konoha instead of carrying Itachi's will..in my opinion he should of went with Itachi after the massacre..maybe then he wouldn't be psycho
There Is Some Sense In What You've Said, But In Terms Of Itachi Being 'Dark And Emo', I'd Have To Disagree; Ever Since He Witnessed One Of The Great Shinobi Wars, The Trauma He Experienced Transformed Him Into A Pacifist. As A Pacifist, He Was Willing To Go To Great Lengths To Maintain Peace, As Seen Through The Fact That He Destroyed His Entire Clan To Prevent A Coup D'etat From Taking Place, Which Would've No Doubt Caused Havoc And Chaos Within Konoha; Therefore, There Was No Need For Him To Feel 'Dark And Emo' Over His Actions, Despite The Fact That I Believe He Did Experience Great Sadness Over What He Did.
On The Other Hand, Sasuke's Entire Reality Was Shattered During The Night Of The Uchiha Clan Massacre - Which Set Him On The Path To Revenge, Which Has Led To His Personality Gradually Becoming Colder And Darker, Manifesting In The Ruthless Sasuke We Watch/Read In The Anime/Manga Today. Yes, It Was His Choice To Destroy The Hidden Leaf Village, But That Shouldn't Be Surprising To Anyone Who Has Seen His Character Development From Part 1 To Part 2 - His Entire Life Has Been Soaked In Hatred And Vengeance [Partly Itachi's Fault], And Even While He May Have Forgiven His Brother, You Can't Expect Someone Who's Entire Life Has Been Focused On Malice And Revenge To Simply 'Choose' A Peaceful Solution, Even If They Were Itachi's Last Wishes.
In Terms Of Sasuke Going With Itachi, I Highly Doubt He'd Be Eager To Follow After Someone Who
Just Killed His Family & Clan.