If someone I don't like is allowed to go somewhere I don't want them to go, they could start killing people at any moment.
Also, I am of the view that every single person south of the border that would want to cross north of Mexico is a gang-affiliated serial killer. Every single person coming from East Asia is a spy, a saboteur, or a left-wing extremist intent on destabilizing the country. Every single African coming to the US has Ebola. Every single Muslim coming to the US is going to impose Sharia Law.
We need to close our borders until I, personally, feel safe. And the TV says I'm not safe. So nobody should be allowed, unless they are white.