The open borders Cato Institute has a brilliant analogy for what would happen if America opened its borders: Israel’s experience when Ariel Sharon invited in lots of Russian Jews (and quasi-Jews):

Does Mass Immigration Destroy Institutions? 1990s Israel as a Natural Experiment By Benjamin Powell, J. R. Clark, and Alex Nowrasteh

January 12, 2017 The relaxation of emigration restrictions in the Soviet Union and the State’s subsequent collapse led to a large exogenous shock to Israel’s immigrant flows because Israel allows unrestricted immigration for world-wide Jews.

Who make up 0.2% of the world’s population. So another way of putting it would be that Israel does not allow much immigration for 99.8% of the people on Earth.

Israel’s population increased by 20 percent in the 1990s due to immigration from the former Soviet Union. These immigrants did not bring social capital that eroded the quality of Israel’s institutional environment. We find that economic institutions improved substantially over the decade. Our synthetic control methodology indicates that it is likely that the institutional improvement would not have occurred to the same degree without the mass migration. Our case study indicates that immigrant participation in the political process is the main mechanism through which the migration caused institutional change.

What happened? Well, Israel suddenly became really good at things like telecommunications software and hacking. And Tel Aviv real estate got very expensive. And Ariel Sharon got elected Prime Minister by the new voters he invited in. And the peace process went bye-bye. And Israel built a lot of fences on its borders to keep illegal infiltrators out. And a lot of the Russians/Israelis moved on to North Hollywood and got jobs as bodyguards for billionaires in the Hollywood Hills.

So this is a perfect guidepost for what would happen if America let in a lot more Mexicans and Muslims.