"I also thought it beyond debate that the secret of the US's success is our system of government, the apogee of western liberalism (the traditional kind), based as it is in faith in the Almighty."
All true, it is also true that part of our success is due to our long history of encouraging and supporting immigration. Huddled masses and etc.
A nice poem, but an irrational immigration policy.
Likewise, just because it was good policy in the past doesn't mean it will be good policy forever. There was a time we had a continent to populate - a frontier to conquer and an industrial revolution to manage.
Now, prosperity is the result of increased efficiency, not increased population.
Those "huddled masses" were expected to have a sponser or support themselves. There was no welfare or socialist services to fall back on.