So do you think that any protest against nuclear war or war in Vietnam were completely useless, because nobody knows what was exact causation?
I do not claim that antinuclear protest was the only cause of nuclear disarmament but I think that it was one of several parallel causes and no we now, neither people at this time could find the proportion. But is some cases street protests are effective. Greenpeace did most of its job by street protest.

Also your example with creating Skype is not correct. Preventing human extinction is not equal to creating one concrete thing (or may be Friendly AI?). For example someone could not prevent war in Vietnam by creating any possible concrete invention. He had to influence government and wide masses of people.

If you are going to be killed you have right to protest against it. Also you said that street action is reflection of powerlessness. But lack of street actions is also reflect the fact that nobody is interested in the topic.