When that bullshit fairy tale about people only pretending to be families gets challenged to a man everybody who is pushing it to the news tries to deflect the question and then just restates it a slightly different way hoping it will slide. There is no damned evidence. If there was a single confirmed case would become a non-stop media circus and milked for all it was worth to justify this madness and even worse measures.
Every statistic from law enforcement agencies in America and around the globe all show that immigrants - legal or not - not only aren't unique or significant contributors to the crime rate but in fact commit fewer crimes than born residents. You're more likely to be killed by furniture falling from a window than an illegal immigrant. Those sanctuary cities that keep getting vilified? Lower crime rates than their surrounding neighbours due in no small part to the immigrant community being far more willing to get in contact with police when they witness something since they're not afraid the cops will invent an excuse to deport them. A city where the people aren't afraid of each other is just safer, period.
Gangs don't want to leave Mexico, that's where their power base is. They don't want to switch to living in a country with a better funded and organized police force and they don't need to fake refugee status or apply to live permanently in the states or cross the border illegally to enter the US for criminal purposes. They visit for a day, do their business, and leave. Typically they're only in the States for easy access to guns. Hell a lot of drug deals don't even require physically crossing the border to move the product anymore. They range from just throwing things over barriers to using commercial drones. And that's all discounting smuggling through established corporate fronts. But does anyone discuss catching the people on the American side of the border doing business with gangs and cartels? No. No the problem must always be from the outside.
The people at the border are trying to get away from the criminals you're trying to dress them up as, they want to live in a country of law and order, they're trying to find jobs that pay enough to survive and police that aren't ridiculously corrupt. They're not gang member, they're running from the gang members.
You really want to stem the flow of immigration? Stop selling the image of America as the greatest and most benevolent place in the world when this shit comes to light. It just isn't true. Start telling people what America's really become. It isn't the land of opportunity, the nation of the self-made, the country of democratic ideals, or the home of the free. It's not ruled by laws that apply to everyone equally, it's not a place where compassion compels neighbours to stand together in their hours of need, it's not an open economic market where any man can profit from grit, sweat, and brilliance. It's not the leader of the free world, a melting pot, or even a particularly nice place to live any more.
It's the land of the only people to truly attack white culture and rob entire nations en masse: White Nationalists. It is an empire of engineered social norms brutally enforced, individuality praised in poem and punished in practice. Worship what you are told, love who you are told, want only the life that is "traditional" or else you are the enemy. The euphemisms that have dominated Republican rhetoric are laid bare and it hasn't hurt them one damned bit. Abandon hope, all ye who enter without the proper pedigree. For even if it costs America her allies, her trade, the strength of her economy, her position of leadership on the world stage and every ounce of respect it has ever garnered, America's new focus is to draw dividing lines and stoke the fires of resentment.
Tell the immigrants of the world that when they perform honest labour for an employer the white man will consider that being stolen from. Tell them that if they start their own business defying the "lump of labour" fallacy the white man will consider that being stolen from. Tell them that when they spend their life savings to receive what is promoted to them as the finest education in the world the white man will consider that being stolen from. Let all know that every individual achievement and invention shall come to nothing, if ever spoken of the details shall be sparse and the blanks filled with white. Tell the women of the world they will have the freedom to be a wife and a mother and nothing else if they're not planning on being both of those things. Heaven help them if they end up as only one at a time. Tell the women of the world that when they speak, the men will remind them to only do so when spoken to. Tell the women of the world that their womb is the only thing protected by law, not their lives or their rights or the sanctity of their bodies, for what grows in their bellies belongs to a man. Man, woman, or child. Everyone shall be put in their place and shackled there. To step out of line or breath a whisper of discontent will be taken as an act of aggression, punishment swift and severe upon the deviant and a thousand others for good measure to deter future ambition.
And while you're at it tell the people of America that even though they were born as Americans, that they've built their homes on her soil and pledged themselves to the flag, that they've worked their fingers to the bone and paid their taxes, that they've carried American values all their lives and may have even have put those lives on the line for America in the armed forces. Tell them they just might not be the "right" kind of American and don't belong in the only country they've ever known. For many it won't really be a surprise. That when you say America first and America for Americans you don't mean "American" as a nationality.