Building a wall between Mexico and the US seems like a very bad idea from several points of view: ecological (this is one continent, and ecosystems don't stop at the boder), political (why do we restrict the flow of labor across this border but leave capital free to cross it unhindered?), social (there are three Native North American nations whose lands are bisected by the border, and the wall increases the difficulty of these Nations governing themselves as a unit or carrying out ceremonial activities and traditional harvests). If we want to end the illegal drug trade, we would do well to help Mexico and central american countries provide decent incomes to their people who work at useful legal jobs, rather than keeping wages low to benefit global corporations; and of course we could legalize most of the drugs that are illegal today and allow production near the point of consumption. If we had a real NAFTA, we'd let workers from anywhere in North America get jobs anywhere on the continent, the way the European Union does, rather than criminalizing economic migration. If we really fear that the growth of Spanish would doom English if more Spanish-speakers were allowed to immigrate, well, as a linguist, I say "Let the contest begin!" By acting on our fears and militarizing the border we are intensifying the problems of inequality that we should be striving to solve.
And then there's the environment. Beatiful and unique types of animals and plants thrive on both sides of the border in the Sonoran and Chihuauan desserts that span that border, and some of them have a very limited range in which they can thrive. Some, like the big cats, need to range both sides of the border simply to survive. As the gaps in the border wall are closed, and as streams of desperate migrants and smugglers are funnelled into ever-more ecologically-sensitive parts of the border, bulldozers and jeeps tear up the delicate arroyos and desert soils, gunfire threatens animals with nowhere to run. I've lived in and loved that part of the world; it's where my Mom grew up. Going into Mexico was a mind-expanding but inexpensive experience when I was young. My cousins have gathered for decades at a beach in Sonora every year; it was there that I learned how to smoke-out wild bees for their honey, which dessert plants were nourishing and which were poisonous, where to find emergency water sources near rock formations. When I was older, I used to go hiking in the sky-island mountains on both sides of the border, watch playful coatimundis, lizards, and colorful tropical birds move through the distinctive Sonoran landscape. I remember the Papago piligrimage to Magdalena, Sonora, where some people crawled all the way from San Xavier del Bac outside Tucson to the old cathedral in Magdalena, and others walked all or part of the way. What happens to the pilgrims at the Nogales border now? Do they have to stand in line for hours and show passports? How do the Jaguars and jaguarundis follow the game across the line? When fishes in the Yaqui River tributaries cross the border at Agua Prieta, are they stopped or poisoned?
Anyway, here are some of the pictures:
The above two pictures are from my 1919 Book of Knowledge. The rest are from sources labelled as public domain by wikipedia, including some from the US Fish and Wildlife Service.