Earlier quoted context omitted.
What protesters were willing to do in the 60s or in 2018 is orthogonal to ensuring that Google maintains a workforce of "moral" people. Suggestions that those who think that Google is going down a dark path should leave will just result in moral evaporative cooling, which leaves everybody off worse.
That sounds like the same excuse that companies and the government used in the 80s when people were trying to get the government to impose sanctions on South Africa over apartheid. Signing a piece of paper knowing that it is of no personal risk to you is virtue signaling. Why should that get a company to change? What will be the consequences if they go ahead with thier plan? A more harshly written letter?
The clear implication is that these people will quit the company if Google goes forward with Dragonfly.