The US (and many nations for that matter) monitor, track, and protect their borders by foreigners and of a group of mathematicians cannot fathom why this may be the case amidst all-time high mistrust, spying, and academic and corporate espionage and then they should've studied harder.
But it is not just about the numbers, you are probably right that statistically, mathematicians don't have much to fear at the border, but the current administration seems to go out of its way make the US unwelcoming. All countries will protect their borders in some way but they usually don't make a show out of it like the US does.
If you go to a hotel and are greeted by a grumpy guy who asks how how you dare book a room on their property, it is a natural reaction to move to the hotel next door where the staff is hopefully more friendly.
<https://thehill.com/policy/international/5205954-french-scie...>
"Korean Scientist With Green Card Detained for a Week and Denied Access to His Lawyer"
<https://www.commondreams.org/news/korean-legal-resident-deta...>
"A US-born NASA scientist was detained at the border until he unlocked his phone"
<https://www.theverge.com/2017/2/12/14583124/nasa-sidd-bikkan...>
"Russian scientist working at Harvard detained by ICE after being stopped at Logan Airport"
<https://www.boston25news.com/news/local/russian-scientist-wo...>
"Chinese American researchers targeted at US border"
<https://concernedscientists.org/2023/03/chinese-american-res...>
These are just cases that make the news. There is a very real possibility of being detained, having devices confiscated, or being refused entry if you are an outspoken critic of the president.
> This comment is devoid of data.
So is yours...