Was it necessary to make confusion?
It was not God who made the confusion, it was humans...
I don't know if it was necessary, only God knows that, but it happened.
Sadly, the confusion is still with us since most people still adhere to the older religions so they are still confused.
The confusion could end now since we have a new revelation from God, but I think it will continue for some time since so few people have recognized Baha'u'llah...
By the way, I am stil planning on answering your post on the Evidence for God thread, I just haven't had time yet.