This has been bugging me ever since the concept of missing-nins was introduced and Orochimaru and Akatsuki appeared for the first time. You see, I've been wondering about the course of action Sasuke would take if he haven't had an (evil)brother, who is most likely(even after his "defeat") still light years ahead of Sasuke in terms of skills. I think that in this case, Sasuke's growth would be "stunted" in a way, and he would most likely be highly frustrated. Yes, as much as this "hatred" business may seem silly, this is also constituting his development. Besides(at least I believe so), since Sasuke's innate personality is highly bent on becoming "the best" and since Konoha is a somewhat "limited" and closed place, I think that Sas would sooner or later learn all(or most) jutsus in the village and then he would have to go to Orochimaru anyway(or leave the village in any direction whatsoever, to train with other people), because Konoha's jutsus would probably be not enough for him.
Yes, although this may seem controversial, I think that villages' policies on missing-nins are somewhat flawed. After all, obviously not all missing-nins are dangerous criminals/people who want to destroy or control the village themselves. I have no doubt that most of these people are actually like the Sannin(or specifically, like Jiraiya or Tsunade) - ninja travelling the world, studying jutsu and not necessarily be involved in dangerous business. Yes, one might say something like this: "but you can develop yourself well in your own village!", but I highly doubt this is the case. We have seen that most of character's development in terms of skills has been achieved during some battles, or during intense training bent on defeating some enemy. So, in this case, if this wasn't for Itachi, I think that Sasuke would still be frustrated in some way. Naruto most likely being too annoying for Sas to handle, him learning all the stuff about village, and generally being bored - heck, his observation would probably lead him to the same thing Itachi did to his clan - especially since Sasuke has good observation skills, and maybe he would go the same path Itachi did.
So, in conclusion, if Itachi didn't exist, and if I was Sasuke, I would either get the fuck out of Konoha, or kill myself due to massive frustration No, really.
(Yeah, this may seem like the usual "what would be if....." thread, but I had to create it anyway - firstly because these thoughts have been lingering in my mind for quite some time, and secondly because I can related to Sasuke's situation in some way)