If they don't think it will change anything, we can agree that this boycott is purely symbolic and will accomplish nothing.
It only helps some rich people feel morally superior. That doesn't impress me much, but I see others find it important. To each their own, I guess.
And even if it is purely symbolic, lots of symbolic actions do more than nothing.
At the very least it may improve employee morale to not support ICE which may increase Github’s employee retention rate, which may not be a big deal for ICE but may be a bigger deal for Github.
And finally, death by a thousand cuts is certainly a thing.
As for “only being symbolic”, no, it wouldn’t. It would allow workers to be in an environment where their work supports their values. A lot of these workers are going to leave the org to go work for a company that doesn’t so conflict with their values, as is absolutely their prerogative in a free labor market. This is actually a mature way to let GitHub understand the full costs of their actions, so that they can make an informed decision. There’s literally no problem here, this is a functioning labor dynamic.