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.
Um, think you've got this backwards. Private entities shouldn't have to take on anyone they don't want as customers (for whatever reason - do you have to justify who you do or don't want in your livingroom?), but publicly-funded institutions shouldn't be able to deny service on political grounds.
Imagine for a moment that things change completely, and the ICE starts refusing to follow the orders of the Government - but now the Government is leaning towards the far-left, and wants the ICE to open borders to all. The ICE would no doubt have a lot of supporters, but disobeying the Government in such case would ALSO be wrong because in a democracy, the Government represents the people - by not following the orders of the Government, you're basically advancing anarchy. In both cases, the correct attitude is to fight for a Government change. It's not democratic for a Government organization to take its own stance on a topic despite the Government's policies.
Denying service to ICE the organization isn't even remotely comparable to denying service to actual human beings.