CBP != ICE. I'm very wary of this recent push to vilify anyone who enforces immigration laws or the integrity of our borders. It seems to be a very emotional, knee-jerk reaction that completely ignores the inevitably serious consequences that would result from lack of border and immigration enforcement.

CBP != ICE, but CBP and ICE are components of a single system. An engineer should appreciate that.

Our democracy has enacted laws that ICE is tasked with enforcing. ICE agents are not really the bad guys here for following those laws -- the American voting public is the problem. Your (and my) representatives made this possible, and continue to allow it, because you (and I) have not made it a priority when we vote.

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.

"Just following orders (to "kidnap" and indefinitely contain people in prison camps)" is not a valid defense

With separation of power between law enforcement and legislative branches of government, it is indeed the job of the law enforcement officers to enforce laws even they do not agree with. Of course, there is a threshold beyond which anyone in deep moral disagreement with a policy can and should protest in a variety of civil ways (including quitting such law enforcement jobs), and this is a normal part of how the checks-and-balances of power works.

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.