khaydz5, you're calling somebody a fanboy with those 'arguments'? That's ridiculous. ;D
Itachi definitely could do something about Chibaku Tensei. The first way would be to destroy it with Amaterasu before it attracts too many stones. Amaterasu even burned fire itself, so it wouldn't take long to destroy the core. And since Chibaku Tensei attracts everything, it'd also attract Amaterasu. The second one would be to burn Pain with Amaterasu while he's preparing or using it, as kadowade already said it doesn't work instantly.
What will Pain do about Susanoo or Amaterasu? None of his bodys except of Gakido & Tendo could do anything about the black flames. If Gakido tries to absorb them from another body, it means that two bodys are distracted, what gives Itachi a good chance to attack. If he's clever (what he definitely is) he'll just aim for their eyes; no eyes means no power, and we already saw that Pain can be easily blinded. Susanoo means death for those who get too close to Itachi anyway (so Bansho Tennin would be suicide for Tendo). It's activated in an instant, that way Itachi was able to block Kirin. Shinra Tensei wouldn't even pressurize it that much, since it possesses Yata no Kagami & even Katsuju was able to protect the villagers from the huge version. With Yasaka no Magatama he even got a strong long range attack. Don't tell me about Itachis bad stamina now; in his battle with Sasuke he used Amaterasu four times (one time for a really long time), extinguished it once (which is quite damaging as we later saw at Sasuke), used Tsukuyomi (which got broken, that took quite a toll, too), kept Susanoo activate for about ten minutes & last but not least transfered his Amaterasu into Sasuke. He'll neither use Tsukuyomi, nor will he extinguish Amaterasu. He won't transfer Amaterasu to Pain either. So, Itachi could do a lot against Pain. Apart from that he's a master when it comes to illusions, and we already saw that they perfectly work on Pain. We also saw a complete stadium being caught inside an illusion, and like Madara said the trick lies in how to use even a small, weak Genjutsu. Itachi's also using tricks like exploding Bunshin or Karasu Bunshin and is pretty skilled with weapons; in the shortest time he was able to find Nagatos blind spot & hit it with Kunai. Not to speak of his speed. We also saw that the hell statue can be easily defeated. Now I gave some arguments, the only real ones since the last few pages. Please answer with real arguments, not that fanboy-bullshit; it just makes you look like dumb children.