That doesnt matter, remember naruto had to defend himself because itachi wasnt on auto pilot then and kabuto was trying to actually capture him, also when in naruto did it become impossible to fight while talking when EVERYONE does it. Another thing is, even so, Itachi still had to keep up with naruto's blows regardless of talking or not and did it.
What do you mean "it doesn't matter"? I don't get how it could possibly NOT matter considering that Sasuke has always been Naruto's objective and the fact that Naruto wanted to see for himself if what Obito had told him was true, it VERY much matters.
We can't just pull stuff out of our asses here. Itachi was fighting to capture Naruto, true. But Naruto at the same time was fighting against an immortal Itachi with unlimited chakra and an undying body. It's kind of the same thing, since neither one can kill the other.
Not to mention the fact that Nagato was there, who is still quite a bit stronger than Bee is, putting team Akatsuki at the advantage in this situation.
As to when did it become impossible to fight while talking?
Well in most fights, talking doesn't really matter. All you are really doing is trying to get rid of a threat. Itachi was only a threat, but possessed information that Naruto wanted to know and Itachi, being a good guy, is more willing to give to Naruto who he had put his trust in. The talking made it conclusive to Naruto that Itachi was, indeed, on the side of the Allied Forces. Otherwise, Naruto may have just fully taken Kakashi's advice and took what Obito said with a grain of salt. I do realize that Naruto believed Obito somewhat, but Itachi made it prevalent that he was a good guy.