Yes it did occur to me. That was then; this is now. Slaves were also imported to help build infrastructure in a country that had none. That was then; this is now.
This country is no longer a vast underpopulated wilderness in need of settlers to populate it. IMO, there is not a shortage of (fatal) disease ridden third worlders in the USA. I don't see the need to import more.
Also, there were indigenous peoples here-the 'Indians' to whom you alluded. How did that mass immigration deal work out for them? Worked out great for the immigrants; not so well for the Indian peoples.
And, KEEP YOUR PANTS ON: The Indians were immigrants too, Siberian hunter groups. Google it. It's a DNA fact.
No, it didn't work out so well for the Indians...also misnamed as Columbus DIDN'T reach India.
Another fact: The American Indians also had slavery, from the tribes they fought with, over the usual, land, power...and slaves.
We don't IMPORT people. That is what the slave-holders did. We ALLOW them to immigrate. I'm sure you see the difference here.
The disease-ridden people? Like those American-born Americans with AIDS? Cancer? Huntington's Disease? Diabetes? Strokes? Lung cancer, both tobacco and non-tobacco related? Alcohol related diseases?
IMHO: Préférable de garder votre pantalon. :o)