They're really not. It is possible to not like (some of) what ICE does and also recognize that they are not rounding up a lawless autocrat's political enemies for torture, indefinite imprisonment and execution.
The immigration police are filled with racists, killers, and white nationalists. This CBP agent was literally a serial killer:
https://www.cnn.com/2018/09/15/us/us-border-patrol-agent-arr...
No one in Nazi Germany could vote to rein in the Gestapo, and the Gestapo did not follow anything resembling fairly applied laws. ICE targets a well-defined legal category of people and follows well-defined legal processes. The Gestapo could arrest almost anyone for any reason and mistreat them however it pleased with impunity. That is obviously untrue of ICE, which cannot tomorrow kidnap Joe Biden.
But you must acknowledge that there are many who do not fundamentally disagree with the underlying laws, at least not to a magnitude such that they believe it is worth protesting. And as such, we have officers who enforce those laws, who have not (at this time) quit their roles.
Therefore, to the extent that one believes this form of government with checks and balances yields more humane results (on average, over time) than one which merges legislative/judiciary/executive power, and to the extent that you acknowledge legitimate moral opinions exist that are different from your own, it definitely can be argued that it's moral to continue enforcing laws you do not personally agree with -- up to a point.
The question is, what is the breaking point where a law enforcement officer protests against a horrible law by refusing to enforce it, quits, or otherwise?
Take almost any politically divisive issue, and you will find there's not a very easy answer here -- especially because each person will have a slightly different moral opinion on the matter.
This one story alone is chilling:
"Diabetic Man Dies After Being Deported To Iraq: ACLU Jimmy Aldaoud reportedly came to the U.S. as a baby and didn’t speak Arabic. He died after he was unable to get insulin, his family says."
https://www.huffpost.com/entry/jimmy-aldaoud-iraq-deported_n...