This one clip, from Douglas Murray's good article, tells it all:
Representative Eric Swalwell, for instance, claims that walls themselves — bricks, mortar, the lot — are "medieval." They are also, he says,"a symbol of 'us and not us.' And that is not U.S."
Out of 7.3 billion people in the world about 7 billion are not "us". That is, they are not US citizens.
The United States cannot allow every one of the "non us" to come to the US, simply because they want to.
That would lead to the destruction of the very US to which they are seeking to emigrate.
