Why did Orochimnaru kill Kazekage befor the attack of Konoha? He would have really been a big force against the Konoha Jounins. With him in the mix, they could have continued with the attack even after Orochimaru's arms got sealed. Orochimaru could have still taken his place sitting up next to the hokage. and their fight could have gone the same way. But then the Kazekage could have come in over the wall with the big snakes and all the other sand and sound ninjas and beat some ass.
Or, are we supposed to believe that Orochimaru killed Kazekage much earlier and Kazekage never really agreed to the attack in the first place.