It would be the first step in a united planet rather than the pettiness we suffer now with individual competing states.

The beauty of countries is that different countries can try vastly different things, and then we can look at the results afterwords and see which countries made good decisions and which made bad decisions.

Until the Chinese Exclusion Act of 1882, there were no restrictions on immigration. And after that, the immigration of white people was still completely unrestricted, until the Immigration Act of 1921. And after which, it was still relatively easy for citizens from Western European countries to move to the US (thanks to the "National Origins formula", up until the Immigration Act of 1965 was passed.

When did the US A) allow unrestricted immigration of people of non-European origin, B) actually have significant numbers of immigrants of non-European origin, and C) not quickly move to restrict that immigration?

Unrestricted immigration of people of European origins is not the same thing as opening up the borders without restriction.

These days, we don't need any more able-bodied factory workers. We are no longer an industrial-labor economy. We need service and skilled labor, instead.

You need to stop relying on television shows for understanding history and read more. There was no "rugged expanse," there was an ongoing Native American genocide. Geronimo died in 1909. The Indian Wars did not end until 1924. As to how much laborers were really needed in factories, Sinclair's The Jungle (published in 1906) is a good illustration.