It's in the damn name. Immigration enforcement. We have a legal immigration process in this country, many try to come here illegally. Without a border, you have no country.
Whatever the policy on the books is, we have a pretty clearly different actual policy resulting from the way ICE chooses to enforce the law: brown people who want to live here are treated strictly and with hostility and white people who want to live here are treated on the whole with more leniency.
You still have a border, just like the 50 US states have internal borders with each other. Why haven't they ceased to exist as discrete entities?
Permeable borders abound in nature. Trying to obstruct the natural behavior of migration is as foolish as trying to halt the tides and arguably causes worse economic distortions than it solves.
The legal immigration process has been slowed to a crawl by the current administration[1]. Any claims that they simply wish for people to follow the legal process are entirely misleading, to the point of being reality-muddling propaganda. The administration is making the legal process harder, impossible in some cases[2], and is advocating for the shutdown of many legal avenues, even those that the president's family themselves have used to attain status here[3].