Why is it that things like this happen ( see the video and comment )?

Things happen like this because - when somebody believes their leaders and follows them into hell - this is the result. The scenes are from Nazi concentration camps - where 6 million jews were murdered, d and used for medical experiments. In total 55 million people died in the 2nd world war - more than 1/2 were innocent civilians - just trying to get out of the way. Read Animal Farm by George Orwell and find out how this stuff gets started. "Some animals are more equal than others".