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.
After Trump took office, I began reading The Rise and Fall of the Third Reich, to be on guard – I was afraid. The ICE camps are evil, scary, cruel, and probably illegal, but not indicative of the sort of fascism we saw under the Nazis. After all, they functioned similarly under the previous US president, who did not seem to have fascist tendencies. As others have mentioned, the detainment of the Uighurs rings much, much closer to Nazi Germany. In some ways scarier.
We have the freedom to leave work and sit in front of courthouses in protest until those responsible for ICE atrocities are prosecuted. We have other similar such freedoms.
Demanding your employer to take a foolhardy action which will register as a minor inconvenience in the target's IT department is... just silly. It's grasping at the closest power center you can find instead of making the effort to find a relevant one.
Saying folks have the freedom to leave their job is ridiculous and only reinforces my point.