A world of free movement would be $78T richer

There's a very good SMBC comic that addresses the "greater pie" fallacy. [1] To summarize: the total economic pie growing and individual slices shrinking are not mutually exclusive.

[1] https://www.smbc-comics.com/comic/2012-04-03

Okay, take the people the OP is talking about, with spouse and children. Then look at their qualifications for work in the US. Look at their skills in reading, writing, and arithmetic, knowledge of English, US civics, etc. Some of the immigrants need training in bathing, using a toilet, and other basic hygiene. And there tend to be serious medical, including communicable disease, problems -- TB, measles, polio, GI parasites, etc. And look at job skills -- computer usage, basics of electricity in factories and on job sites, skills with important work place tools, etc.

The US has long had immigration criteria that ruled out such people.

Okay, now take a US citizen that on qualifications is a good match for such an immigrant and see what their job and career prospects are. As we know very, very well, they are unemployable or nearly so. Well, so will be the immigrant. The ability of the immigrant to get a job, have a career, and support themselves and their family is from poor to zero.

So, why do such immigrants want to come to the US? And how can they hope to make it?

First, the usual way has been the immigrants were young men who left their families, friends, villages behind and did common labor, e.g., picking fruit. They lived several to a room sleeping on a mat on the floor. They were here only the warmer parts of the year, not through the winters. They got paid in US cash with no deductions for taxes or US Social Security. Then at least for the winter, they went home and took their US cash with them. Due to currency value differences, their US cash would go really far back in their home village. Of course, that whole situation is wildly illegal, on taxes and more. A US citizen here for 12 months a year can't do that and support a family or even themselves.

Second, if the immigrant brings their family, with children, then the family and especially the children are one heck of a huge expense for the US education and welfare systems, paid for by US workers paying taxes.

More broadly the OP does poor accounting: Sure, there are a lot of people in the world who are, in US terms, not very productive. Some of these people are current US citizens, and the US is struggling to get those people trained, into jobs, and productive. The US has many dozens of job training programs. Those candidate immigrants are on average less well qualified than the millions of current US citizens struggling to be productive in the US economy. Where do the OP authors get the funny stuff they've been smoking to conclude that immigrants much less well qualified than millions of US citizens who are already struggling to get good jobs in the US will do better than those already struggling US citizens?

Or, if those immigrants are such a valuable, neglected resource, then, sure, take some US tools, supplies, know-how, etc. to some foreign countries and give the people there jobs. Chrysler tried that in Mexico and has decided that it was a mistake and are returning to Detroit.

Uh, apparently to make people as productive as in the US takes more than just some people and training for a job; also required are huge investments in infrastructure from water and sewer, roads and bridges, suppliers and supplies, communications, regulations, laws, law enforcement, public health, medical care, citizenship, ..., the whole thing. The OP is being simplistic, straining over gnats and forgetting elephants.

IMHO, too many powerful people in US business see the immigrants as a new version of slave labor. In 1861, the US had a lot of slave labor and people who liked that situation; we fought a bloody war over that issue, killed IIRC 600,000+ US soldiers and maybe a comparable number of other US citizens. Net, slavery was a big mistake. Bringing back slavery will be a bigger mistake. The forces in favor of slavery have been strong for thousands of years and did not end in 1865 or so.

If the authors of the OP want to take some funds, rush to some country with lots of really poor people that are unproductive, set up some businesses, give those people jobs, training, etc., so be it. People have been trying that off and on around the world for a long time. We've long had international organizations for such development. Successes have not been anything like the claims of tens of trillions of dollars claimed in the OP.

So, the OP looks like really bad, simple economic and business arithmetic, so bad the OP does not look like economics. So, what really is the OP? Hmm .... For a candidate answer, consider the advice "Always look for the hidden agenda.".

"immigrant-friendly" thats very far from being accurate.

edit: strong lang.

This is really just propaganda.