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.
Most of the comments here seem to indicate that what was said, and proposed to be done, is political, and politics are bad. This seems to rest on the assumption that one, institutions like ICE are politically neutral, and/or two, simply doing business with a political organization is necessarily "apolitical." It also relies on the assumption that anything that can be identified as political is off limits to businesses, and that many businesses are capable of avoiding being "political" altogether.
Businesses can be largely nonpartisan, but they almost certainly cannot avoid "politics." It is very difficult to be consistently "neutral" on issues like racial justice and equal opportunities for LGBTQ folks. Is hiring a trans woman "political?" Is simply doing business with a political campaign entirely apolitical? When we look to issues of the past, is/was supporting the Civil Rights Movement political? It certainly seems like a totally different type of politics than the kind where you take a partisan stance on economic policy.
IBM rightfully faced backlash for doing business with government institutions in the 20th century that were clearly not neutral on the issue of racial justice. The IBM example isn't to compare that situation to the current, but to demonstrate that you cannot justify an apolitical position in all contexts, and that "apolitical" positions may not be quite as neutral as it appears on the surface (hopefully that avoids a Godwin's Law violation.) Similarly, while to a lesser degree, ICE as it exists today can clearly be identified as an agency carrying out a specific political agenda that has a negative effect on racial justice. If doing business with an institution furthers that organizations' goals, and those goals are not neutral on the issue of racial justice, it certainly can be argued that your continued business with that institution furthers that organizations' goals. To argue otherwise puts one into a position where it seems they'd have to defend IBM in the aforementioned example for logical consistency.