I don't know. I have always thought they needed to get people out due to the disease factor and such. But the pictures they were showing were of dry areas. They showed the "guards" going through any open houses etc. If the area was flooded then I would understand if they were checking for trapped people. Perhaps they are searching for people in hiding or something. I don't know. It was bizarre to see this on American TV.
They are clearing out the guns and the people because the city of New Orleans is soon to become the seat of power of the One World Government. Once everything is in place the Beast will rise out of the fathomless Pit and take the reigns of power and rule over the entire Earth. It's gonna suck big time.
Maybe the problem is that even with the dry areas, what with the overall infrastructure compromised, and few services and businesses operating, they simply want to evac the whole city until they get the mess more sorted out. I will give the benefit of a doubt at this point.