Why did Itachi use Tsukuyomi on Kakashi?

[Kakashobito]

Why did he use it? If he was on Konohas side?

[Kages]

Pretending like he's evil.

[-Raviel-]

He had to send a message..*whisper*he solos

[Hacker.]

Because he was an Akatsuki Member. And he is not on Konoha's side. He simply trusted the Village, he really cares for his Brother. The people of the village do not matter to him.

[Kirabi]

He had to play a role, make him self look like a villian. Tsukiyomi only renders a target unconscious, so he did another option that forced Kakashi to be unable to move.

[HashiramaDescendant]

He's a great actor. :y

[Chiharu]

Kisame was there so Itachi had to be convincing.
And he probably knew that tsukuyomi wouldn't kill Kakashi.

[sasukexx13]

A true Shinobi

[Becareful]

Pretending like he's evil.

This is probably true

[Shadowkiller56]

Because it's like the only thing he could have done to Kakashi, without injuring him too heavily.

[PainTotheEarth]

because kakashi was in his way

[Dance of the Willow]

The people of the village do not matter to him.

Okay, so that's why he killed his entire family (with the exception of Sasuke and Obito) for the sake of the Leaf, and because he was ordered to. That must also be why he programmed Shisui's eye to make Sasuke "protect the leaf", and even if that failed, it was still his original intention.

[Kakashobito]

Because he was an Akatsuki Member. And he is not on Konoha's side. He simply trusted the Village, he really cares for his Brother. The people of the village do not matter to him.

He does not care for the village? Wtf? He threw his Life away for the Sake of the village

[Itachi Rane]

either kishi wanted us to believe he was evil or maybe itachi wanted to show kakashi his powers so that kakashi knows the extent of itachi's genjutsu abilities and thus trains to be prepared enough in case they meet again....

[vegetaHATAKE]

He was pretending in front of kisame .....he's an awesome actor

[EliteKakashi]

He ordered Kisame to capture Kakashi and kill Asuma and Kurenai.

He clearly didn't care much for the 3, on the Leaf's side or not.

[noni1997]

to act like he was evil and also for him to get so scared he wouldn't try to fight him anymore

[Makarov]

The answer is above but because since Kisame is an Akatsuki member so itachi had to make a scene for it to look he doesn't care about the people of Konoha but he actually trying to help and he cares for his brother Sasuke.

[Serotonin]

Like most rational people here.

I agree It was probably for Kisames benefit.

[Staarkk]

He wanted to see if Kakashi was powerful enough to protect/train Sasuke, so he wanted to see how strong he was in all aspects of combat including Genjutsu.

[avenged sevenfold]

he had to play the villain to keep his ruse up

[Owarij]

Had he not used it?
He'd have had an all out fight with kakashi, which may have ended in an even worse scenario that what happened.... In an all of fight there's no guarantee he could ensure kakashi came out alive.. moves like amaterasu etc may have been used...

That was the best way to get Kakashi out of the fight and not kill him

[Cowthulhu45]

He was acting for kisame, and we needed to see just how OP he was. One shotting kakashi does that.