What Are there Undesirable cultures and people, we should be careful allowing in the US?

Criminals, terrorists, illegals.

Anyone who isn't white should be excluded from entering the United States. White people like me don't want anymore non white people coming into the United States.

Muslims & socialists .........................................

"Undesirable" people would include those with serious criminal records. But the more "undesirable" a culture is the more likely the US (historically) has been to take people from that culture in for their own protection. The fact that Soviet defectors were welcomed but now would be Russian immigrants have a hard road of it is mute testimony to how the US has used geopolitics to determine who is and isn't worth importing.

Racists who think an entire culture could be categorized without knowing the individual.

Shouldn't that be, "What are the undesirable cultures and people we should be allowing in the US?"?

Racist, ignorant, natural born whites.

Definitely racists.