I can see both sides:
Yes, Google offices are private property.
Yes, Google is an American company - if Google's employees don't agree with an American company serving America and its allies - Israel has been an ally for a long time - then, they should leave for more agreeable pastures. They can even remove Google from their resume once they've found a better resume brand.
However, If I were an employee at Google, and my company had begun serving DoD / IDF against my wishes - then, I would have a better chance of changing this from inside the company than from outside. So, speaking out internally against taking on undesirable customers seems like a more effective tactic than quitting.
But, by protesting in the way they did, they've likely ensured that they will no longer be inside the company.
However, If I were an employee at Google, and my company had begun serving DoD / IDF against my wishes - then, I would have a better chance of changing this from inside the company than from outside. So, speaking out internally against taking on undesirable customers seems like a more effective tactic than quitting.
But, by protesting in the way they did, they've likely ensured that they will no longer be inside the company.