In the interst of balance...

History being what it is, how can Americans justify keeping
"illegals" out? Every single one of the old immigrants was treading
on Indian toes, killing them, drugging them, using starvation and
biological warfare against them to steal their land, only to turn
around and claim squatter's rights?

It's hypocrisy.

Psssst Terry....you need to study history a little better. There is strong
evidence the Indians killed off earlier civilizations using the very
techniques you mentioned. They also had no qualms about killing each other
in what ever horrible method they could think up.