I don't think Kishi has a message with Itachi - I think he's used primarily as a device to shock Sasuke and rearrange his assumptions. It sets up Sasuke's hatred for Konoha, which is essential to the series and sets up the final conflict between Sasuke and Naruto.
I've noticed the thread I posted last night which started this entire discussion has been removed. I guess having the opinion that someone killing their family to prevent an inevitable war from occurring - 40,000 ninja have died in this war - is considered "trolling."
If all we did on this forum is agree with each other it would be pretty boring.