“Why shouldn't people who violate federal law not be arrested?”

this is also one of those times that the civil vs criminal distinction is flattened.

as in, not all violations of the law merit arrest. that's why we have civil penalties. like if you misfile your taxes, park in the wrong spot on government property, make a wrong turn on a forest service road, or otherwise engage in some kind generally harmless activity that is, by statute unlawful, unknowingly or without malice due to the necessity of the moment.

this is a distinction anti-immigrant CHUDs never want to grasp. which is why I think people who want undocumented people locked up "for breaking the law" should all be audited by the most ruthlessly, stick up the ass, pencil pushing automaton. and if anything can be construed as not lawful, they get their door kicked in at 2am, have their house torn up, and be black bagged to whereverthefuck.

because they're illegal.

what are we, some kind of fugitive slave act?

They were asking a rhetorical question. They agree with arresting runaway slaves.

I hope this is a bit. It is too perfectly ignorant and specific.

Federal law is magic and always right -distressingly common belief

People conflating legality with morality really gets under my skin. And it's so prevalent in media it's just enraging.