actually no, he was going to kill Asuma, Kakashi and Kurenai the moment they discovered why he and Kisame were there (for the Kyuubi/Naruto) until Gai showed up.
Itachi is my second favorite character in this series but, we all know that he wouldn't mind getting his hands dirty every now and then :
1. he gave his chakra to kill Gara.
2. killed an entire clan.
3. was going to kill Kakashi and the rest if Gai didn't show up.
this excuse doesn't make any sense AND Itachi had one last Amaterasu in him so why didn't use it on Jiraiya if it was that simple ??
OT : Itachi wasn't scared from Jiraiya but, we have two explanations for what happened, either Kishi was seriously implying that Jiraiya can infact take on both of them (in part 1) or people don't really get this Manga/what the writer is trying to say and use logic that doesn't apply to this series.
Itachi's a shinobi. That's pretty normal, they all get their hands dirty at one time or another. The three points you stated are entirely irrelevant to the topic of this thread. For the first, he couldn't blow his cover as a double spy and Deidara had already captured Gaara-if Itachi refused, the Akatsuki would likely kill him anyway and they'd just find a replacement. The second, his clan was going out either way, whether he raised his hand against it or not. The third, he told them twice to stay away from him and even Kakashi was wondering why Itachi didn't kill him, when he easily could do so. He was only willing to kill them after Kakashi started blabbering on about how he knew the Akatsuki's plans and Kisame was standing right there...what was Itachi supposed to do? Tell Kisame that they should leave right after Kakashi made those statements?
The logic does apply to the series. Itachi was a Konoha shinobi, he didn't want to take down one of their strongest ninjas if he had a chance to avoid it. He took his chance and left. It's completely illogical to think that what Itachi said was true.
This was literally what was said:
Kisame: "But why is this a retreat...for
you?
Itachi: Even with backup, we wouldn't win.
^Does this really sound true? Itachi+Kisame+other Akatsuki members would all get beaten by Jiraiya? I don't think so. Kishimoto wrote for a reason Kakashi wondering why Itachi didn't kill him and later on Obito's statement about Itachi being there not for conflict, but just to make sure that Danzo heard of his presence.