You realize that not everyone in an organization would have agreed with not working with Nazi Germany either?
IBM literally sold them information retrieval technology they used to keep track of concentration camp inmates. So clearly the important decision-makers did not agree.
I guess it is like any other question of what an organization should do. Those with the power to make decisions will decide based on some combination of their own ethical standards or (more likely) what think they is "good for the business", where PR as well as employee morale are components of that. The employees without the power to decide directly can organize to try to convince those with the power to make decisions of the correct ethical choice, or of what's good for the business, or to try to change the calculus of what's good for the business by effecting PR and employee morale etc.
I mean, this is kind of just a description of how human organizations or collective decision-making works....
I personally think that what ICE is doing is absolutely immoral and unethical, putting people, including asylum seekers, into (yes I think it's appropriate language) concentration camps, without a trial or hearing or access to a lawyer, in unsafe conditions (covid makes this even more extreme), separating children from parents, etc. If we looked for an external arbiter of this, I think it also clearly violates international law and agreements on the rights of migrants and refugees, so that could be another argument, don't sell software to organizations that will use it to violate international law.
I personally wouldn't at this point call for github (or anyone) to avoid business with the federal governmetn entirely -- just to avoid your products being used for the programs that are violating international human rights. That is, avoid doing business with ICE, for sure. Maybe with DHS in general, or particular programs/units in DHS.
I can't make you agree. People disagree, this is part of human life. But if I were in github, I'd be working to convince other co-workers of this, and to convince decision-makers leaders of it, as those in the article are presumably doing (I still can't read the article because paywall, so I'm only guessing as I think most commenting are!) This is how humans in organizations work.