They can quit. They can speak out. They can organize. They can petition for change. They could join the more ethical competition (if one exists), or start their own.
This is especially easy to do for employees of a company like Google, with excellent job prospects and often enough "fuck you money" to do whatever they want without serious financial hardship.
They are not hopelessly chained to the corporate profit machine. They can revolt -- that is, if their morals are important enough to them. Otherwise they can stay on and try not to rock the boat, or pretend they don't know or are helpless to act.
A handful of Google employees chose to act and publicly express their objections. This action got results. More employees in companies which act unethically should follow their lead.