The arrest of Rumeysa Ozturk, the Turkish PhD student grabbed off the streets of a Boston suburb by immigration agents last Tuesday, marks a new low in Homeland Security’s overzealous pursuit of ever-larger deportation numbers.

The video of Ozturk’s arrest reveals a violation of basic civil rights and decency that should sicken every American and frighten legal immigrants to their core. For the Trump Administration, it is another leverage point to bring universities into line while also throttling another avenue of legal immigration.

The scene itself resembles one out of a small paramilitary country. An unmarked vehicle pulls up. Masked agents in plainclothes emerge. They accost Ozturk, who utters a small scream. One agent wrests her mobile phone out of her hand. With stunning swiftness, she is handcuffed and escorted away.

Ozturk, a former Fulbright scholar, has been charged with no crime so far, according to her lawyer. Her only infraction appears to be a fairly mild op-ed piece she co-wrote with several other students for the Tufts Daily, in which they urged the university to take seriously a student government resolution calling on the school to divest from companies dealing with Israel and recognise genocide of Palestinians.

In other words, a classic nonviolent exercise of free speech.

Tufts president Sunil Kumar said in a statement that Ozturk’s student-visa status had been terminated “and we seek to confirm whether that information is true”.

Border tsar Tom Homan, who earlier said he was intent on removing the most dangerous undocumented criminals from American streets, has now descended several rungs lower, snatching international students here legally, who reasonably thought the constitutional right of free expression included them.

This makes Ozturk the latest known target resulting from an edict issued by President Donald Trump in January that declared college students who were “Hamas sympathisers” would have their visas cancelled. He also claimed that college campuses “have been infested with radicalism like never before”. (Officials have not presented evidence that Ozturk supports Hamas.)

There have been other arrests, most notably former Columbia University student Mahmoud Khalil earlier this month. Khalil was a leader of pro-Palestinian protests on campus. His green card has been revoked and he faces deportation. Trump said at the time that Khalil’s arrest would be “the first of many”.

That seems to be true. A new effort out of Secretary of State Marco Rubio’s office, “Catch and Revoke”, is reportedly using artificial intelligence to scrape social-media sites for clues about foreign nationals who are possible terrorist-group sympathisers. His office is not the first to use such techniques, but applied broadly and by an administration eager to push limits, they can be dangerous tools that deserve more scrutiny. Rubio said this week that he has revoked some 300 visas — “it might be more”.

There will be other repercussions from cases such as Ozturk’s. Public and private universities in this country depend on international students to add diverse perspectives and broaden the horizons of campus life. Those students also typically pay top dollar.

Now, international students I have talked to are questioning whether an American education is worth the risk. Many are among their country’s best and brightest. They often come from well-to-do families who now are worried sick their children will be caught up in an anti-immigrant movement.

One of the most disturbing aspects of Ozturk’s case is that she obtained a federal district court judge’s order barring her removal from the state of Massachusetts for 48 hours after her arrest. Nevertheless, Ozturk was transported to a detention centre in Louisiana and neither university officials nor her attorney were able to communicate with her.

So that’s that? A promising young doctoral student’s academic career is cut short, perhaps ruined. She faces deportation to a country dealing with its own unrest over civil freedoms.

But the US is not a police state, where one can be whisked off the streets by authorities, as was so common in El Salvador in the 1980s. There individuals were “disappeared” by the tens of thousands, never heard from again.

This country has a process for dealing with those who disobey our laws, or who violate the terms of their visas. Even accused immigrants are due their day in court.

If free speech does not apply to undocumented immigrants, or to legal visa holders, or to those with green cards who are permanent residents, who qualifies? Is it just the precious circle of Americans born here? And when does the Government’s displeasure turn on them?

This country is supposed to set an example for the world. Tightening border security and cracking down on terrorists are worthy and necessary goals. Seizing and detaining lawful immigrants over op-eds? That jeopardises us all.

• Patricia Lopez is a Bloomberg Opinion columnist covering politics and policy. She is a former member of the editorial board at the Minneapolis Star Tribune, where she also worked as a senior political editor and reporter