Politisizing your job is a good way to lose it
Google likes to have a public perception of an ethical employer but underneath all of that they're still an employer that's running a business. Trying to stir up problems because they've got a CBP contract and you don't agree with CBP policies isn't going to change company policy but it will cause you problems.
CBP is an arm of the Federal government and its contracts are like any other government contracts. Legal. You may not agree with it but your choice is to either not work on it -- if possible (and I'm sure Google would accommodate you) or find another job.
Whatever your opinions on immigration policy the people of CBP are charged with administering the law as it is. Its the same deal as the UK's Border Force. Every country has immigration law and people charged with enforcing it, even those countries that are currently major sources of emigrants -- where I live we get a lot of people from Mexico but I can't just decide one day to up stakes and move to Mexico, without a DNI I can't do anything except be a tourist.