I'm no fan of ICE – a very large percentage of my friends in the US are immigrants, and I generally want my country to be a welcoming one. ICE has certainly committed unethical and probably illegal acts (probably true of most federal agencies).
But to expect that a _federal agency_ will be denied service from a private entity, especially for essentially political reasons, is lunacy. It'd attract extreme negative attention from the rest of the government, and great fear from all paying customers that an internet mob could separate them from their code at any time.
We should absolutely be lobbying hard for changes to immigration law, the restrictions placed on ICE, and justice for their wrongdoings.
But I can't see how this helps improve immigration, and it certainly seems likely to cause a lot of negative consequences for GitHub. The employees are putting their employer in a "damned if they do, damned if they don't" situation.
EDIT: Just to clarify, I love the vision of a world where executives don't take actions their workers will protest. I think that in order to get there, the protests need to be reasonable, and I think this one isn't.
EDIT DISCLAIMER: I own a small amount of MSFT stock, which was not on my mind as I wrote this. I use GitHub's free service and have no other relationship I can think of with MSFT or GitHub.
Github refuses to work with ICE today and hypothetically tomorrow will only host code for Democrats? I'm certainly no fan of ICE, but I'm also not sure I like ceding even more control to corporations. Perhaps I'm naive in thinking we can still fix the US through voting.
I can imagine a more disturbing (possible) hypothetical: the activists are successful, and Github terminates it's ICE contract. Nobody else will host their code. ICE still has source code that needs to be hosted, so they hire more developers to maintain their own internal source-code repository. Those developers are subsequently blackballed from future employment opportunities due to their past association with ICE.