Germany did not just go in a round people up. They set up check points where everyone had to be searched for there safety. They also disarmed the population. An they carted away people that might fight back one by one accusing them of crimes. Then once the people had no real power to rise up, then the bad stuff started to happen.
Also remember we rounded up the Japanese in the US an put them in camps too. Do you think everyone knew how they were really being treated?
So you think the Nazi camps were the same as the Japanese camps here ? Were they mistreated here ?
You need to recheck your history. One of the first things they did was outlaw Jews owning a business. Do you think they could do that here ?