First of all, the immigration laws aren't rational. The states aren't "legal" and "illegal", but "documented" and "undocumented". It's often the case that The Official Way To Do Things can cause you to transition from a "documented" state to an "undocumented" state and back again while in the country. Part of what people like the author are trying to do is to help people who made the documented -> undocumented transition to complete their undocumented -> documented transition before ICE an export them somewhere.
Secondly, ICE has basically been given a target of 500k people to expel. They've always had a reputation for being more on the "bully / asshole" side than normal, and now those people have been given a blank check to crank it up to 11.
Finally, there are clear, documented cases of ICE breaking the law and then trying to play games to get around it. Go look up the Abrego-Garcia case:
1. He came in legally, and was documented -- he had a court order forbidding him from being extradited to El Salvador, and was checking in regularly.
2. They swept him up, erroneously identified him as a gang member, and shipped him out to El Salvador before anyone had a chance to do anything to protest
3. They admitted in court that extraditing him was a mistake; but then said, "Well, he's out of our jurisdiction now, we can't do anything to get him back."
4. When, after months of wrangling, they finally did bring him back, they decided to charge him with a crime for something he did years ago (even though they didn't decide to charge him with anything back then, and had plenty of opportunities to do so earlier).
So basically, 1) The immigration laws are broken: not just and not really follow-able 2) ICE often don't follow the law unless browbeaten by the courts to do so 3) they often try to entirely avoid the courts by playing jurisdictional games.
There's a good reason that large numbers of intelligent, dedicated patriots are organizing to oppose ICE.