It may feel better to watch and yell from the outside, and you may have the moral high ground in doing so. But change happens from the inside. We need more companies like GitHub working with agencies to reform their policies.
Also, change is slow. Protests are step one, but there are probably 235 more steps until change is realized. Slow and steady, my friends.
EDIT: To answer the questions about how a company influences policy. Companies influence policy all. the. time. Look at ALEC[1] look at PACs. Look at the fact that Microsoft is not going to be offering facial recognition tech until privacy protections are passed. Not saying ALEC is good, but it exists.
[1] https://en.wikipedia.org/wiki/American_Legislative_Exchange_...
"Hey, you see this part of the code where you sort through the parents, to separate them from their children? Maybe don't do that?"
ICE is going to ignore any unprofessional suggestions, that's not what they hired GitHub to do.
In fact the usual argument employers give when you don't do exactly they hired you to do - "that's not what we hired you for" - is pretty strong. And unless GitHub sabotages their own work (which they won't), then their work will simply be in service to ICE's goals. There's no room left over for contributing non-work opinions.