[jltsiren]

In Finland (and I guess in some other European countries) deportation in itself is not a sufficient reason for arrest. Once you have been informed of the decision, you get some time to leave voluntarily, or to challenge the decision in the administrative court system. But you won't be arrested until the decision is final and you have failed to leave voluntarily, unless there are specific reasons to the contrary. And those specific reasons are typically ones that would justify arresting a citizen as well.

[tgma]

I believe they are free to challenge the decision in an administrative court in the US (under Attorney General, not an Article III court) but they can be arrested. In any case, most countries would reserve the rights to kick you out. That's the deal you make with the country when you choose to get their visa and go there.

[jltsiren]

I don't think the controversy is about deporting people who are no longer wanted in the country. It's about the use of unnecessary force. The principle of minimum necessary force is pretty integral to Western societies. It includes the idea that the authorities are not allowed to arrest anyone until more reasonable options have been exhausted.

[tgma]

Unless there is an imminent threat or you want to send a message and act as a deterrent.