No matter what, the uchiha were going to be massacred, it was ordered by the "higher ups". At least Itachi managed to save his little brother. But looking back on it, Sasuke didn't turn out too great. But it gave Naruto a goal, a rival, a best friend, then an opponent that pushed him towards his full potential. (a bit off topic, but thats the domino effect for you)
Without Sasuke being who he was, Naruto would never have soared to the heights he achieved, Sasuke was the sources of his determination. Itachi's actions led to that, unintentionally, but it still happened.
Finally, Itachi is a good guy who sacrificed his humanity to prevent what probably would have been a bloody civil war.
I hope I didn't miss any effects that were caused by Itachi killing his clan. (though i probably missed a few)