Why did itatchi kill his clan

[Yokurama]

So why do you all think Itatchi killed all the uchia's was it really just to test his strength or do you think there was some alterer not stupid motive

[d_one]

I guess it's because he doesn't want another member from Uchiha Clan Inherited Mangekyoushi Sharingan.

[Guyrif]

Nah...if that was the real reason then he why he left sasuke alive...=z
my theory is that after he Inherit the Mangekyoushi Sharingan he Killed everyone from the Uchiha Clan To test his new Power and to ensure that sasuke will be his life time hater..

Spoiler

but who knows...maybe we'll found out the real motive when Itchi and Sasuke will meet head to head in the Old Uchiha district

[nit3mar3]

i´d say for the pure fun of it, but maybe i´m being sarcastic...

[MiBuKy0ShiRo]

what i do remember is that to inherit the mangekyiou sharingan, the person must kill the 1 that he most love/closed to him. in my thoughts there might be 2 storyline here:

1.he might have follow that theory by killed each person of his clan but still didn't inherit the sharingan till he killed his own family. He do not kill sasuke anymre bcuz he already inherited that from killing his family.(in this case, the family is the 1 closed to him)

2.his victim no.1 is he's own best friend. mybe he inherit the sharingan from this killing. then he tried his new ability by tested it to his clan and let sasuke alive to hatred him or to let his own brother to gain the sharingan by killing him bcuz he loves sasuke. (well this 1 is kinda weird)

P/S: as far as i noe,using mangekyou sharingan used a lot of chakra and it need the user to have plenty of rest in order to use it again. if he used the mangekyou sharingan to kill whole clan,sounds not possible cuz the technique is a direct technique to only 1 victim. so did he use his new sharingan to kill whole clan? dun think so. maybe not cuz of test but for other reason.

[Shinta]

he obtained the Mangekyou Sharingan by killing Uchiha Shisui. he didn't need to kill anyone else for it.
he said that he did it in order to test his "container". that could mean either the MS, or, more likely, his power or potential.
he might've tested the MS on one of the clan, and had to get rid of the witnesses. in that case, he spared Sasuke's life because he wasn't a threat to him.
the more reasonable explanation, which fits better in the story, is that he wanted to test how powerful he really is. and the only way to do that is against the most powerful clan in Konoha (or the Hokage, but he probably didn't want the whole village on his tail).
another possibility is that he felt the clan is too weak and is holding him back from fully exploiting his potential (and according to the facts, he has a point), which also explains his joining Akatsuki.

[kiltev]

shinta's answer is perfect, by the way its kinda what i had to say just in other workds, this discussion is over, this is one of the things that masashi didnt tried to cover from us.
~CLOSED~