They have been effective for millenia, even before democracy. The only thing ineffective now is people saying so. With all the evidence in the world that protest works, people bizarrely disarm themselves.
The targets of the protests take great pains to convince you of it; that should tell you something. They'll bluff until they lose.
It has been ineffective. We've seen peaceful protestors smeared, and beaten and harassed by the police. We've seen counter terror laws abused to smear and arrest leaders. We've seen clampdowns on what protests are allowed to go ahead, and at least on the UK they are pushing and pushing for "tougher" laws to crush protests.
Protest movements are only effective when they present a viable alternative to a more radical movement with a will to violence at their flank. We saw this clearly in the indian independence & american civil rights movements, and the fall of apartheid. Iraq war and climate movement are what you get without the credible threat of violence behind or beside your peaceful protests.
One important lesson of the iraq war protests now that we can see with hindsight: we were right, and we were justified in using much more radical tactics than we actually did. Those horrors lay partially at our coward feet so let's not allow ourselves to be convinced to repeat it with palestine.
You are your opponents' dream. They couldn't write a better script for you - quitting and self-defeating, at the same time!