I get what you and dang are saying, but I'm not so sure it's that simple. If I follow this idea to its logical conclusion, I'm left with simply nihilism. You can use this same reasoning about anything. Why go out and march or protest or do anything for ____ (insert any cause here)? Any single action you do is unlikely to solve a big problem. But everyone can't just give up on everything and go for a walk when things seem hopeless or unlikely to change.

Social pressure is an important phenomenon and public opinion can really end up changing a lot over time, and I'm not so sure it's useless to add numbers to your side of an issue and contribute to a sense of societal consensus. It seems very difficult to pick out exactly what kinds of actions move societal opinion over time. E.g. what were the singular actions between the years 2000 and 2015 that were able to shift opinions on gay marriage so dramatically and make it so widely accepted now in America? If everyone that was fighting for this cause over that time had assumed it was hopeless and just given up and gone for a walk instead, it's possible this shift would not have happened.