Explain in less than 100 words what advantage we gain
from leaving the EU, without mentioning either the EU
itself or any of its rules.

A Nation has to protect its citizens or subjects from threats from outside the Nation and threats from within the Nation. If there are terrorists for example, in any European Nation, then that Nation has to find them and deport them to protect her citizens.

Anything which stops a Nation protecting herself, is anti, not pro that Nation.

Christina