Yes, partitioning Iraq would help reduce the violence, because the different sectarian groups would not feel like they are being controlled by another group. Without a power struggle, each group would be able to live in peace, knowing that they determined their own system of government. It would make the area of Iraq more peaceful.
Considering Iraq has been in some sort of civil unrest for the last two thousand years, it
is unlikely that creating borders will help the situation. Every sect will wish for the reunification of their former state. It would create an atmosphere that idolizes some of their most brutal leaders. Every sectarian group would have a voice, and they would all want to be heard above the others. It would actually increase violence.