If the principle you are referring to is unchecked immigration, that has never really been a principle in the US, even going back to the Ellis Island days. Alcohol, deer running across the highway, and bathtubs are currently more deadly than terrorist attacks. You can be sure that there are people that want to nothing more out of life than to change those statistics, and there's no reason to make it easier for them to accomplish their goals.

The same people probably also want to curb Gun Violence?

Terrorists generally don't want to curb gun violence, no.