Black markets have extraodinarily pernicious effects on those involved, particularly on the supply side. By preventing buyers and sellers from coming together, governments create a large arbitrage opportunity for those willing to engage in black market activities, in this case, jump the US border.
This in turn puts those involved in such activities outside the rule of law and vulnerable to the entire range of adverse events, including arrest, predation and accident.
Hard numbers are difficult to come by. Based on publicly available data, we estimate that nearly 1 million Central Americans and Mexicans will attempt to cross the US border in 2019. Perhaps 10% of these will turn back before ever attempting to cross the border. Of the remainder, we expect 600,000 will be apprehended at the US border, and another 140,000 Central Americans will be detained in Mexico. Most will be quickly deported, but 100,000 will spend several weeks to several months in detention.
These are the comparatively lucky ones.
Approximately 400 migrants will die in the US desert in 2018, and perhaps another 600 in Mexico. Over 100,000 migrant women will be raped, and another 20,000 trafficked into forced prostitution. Another 150,000, primarily men, will be assaulted and robbed, and at least 20,000 will become involved in drug smuggling, many against their will. About 20,000 migrants will fall victim to kidnapping or extortion.
Overall, about 550,000 of the 1 million migrants who begin the journey to the United States will experience an event which the vast majority of Americans would consider traumatic. And this excludes the half million migrants who will be arrested and detained, but quickly released, by US or Mexican authorities. Statistically speaking, every migrant will experience an event which would traumatize the ordinary American.
It is not an exaggeration to describe this situation as the largest on-going humanitarian crisis in the western hemisphere, and the largest in 2018 outside Venezuela. It ranks among the top handful of humanitarian crises in the world, and virtually all of it is the explicit result of US immigration policy.