This statement sounds a little defeatist and gives an excuse for not participating in demonstrations (since the required massive scale is likely not reached, one might be better of not going).
Actually demonstrations, even if they do not effect immediate change, will still have a number of positive outcomes. First, they will likely be reported on in the news (at least that would be the case in Germany), raising awareness. Second, demonstrators will meet like minded individuals with whom they can network and form strategies. Third, demonstrators will realize that they are not isolated and feel more empowered as a result. Last, it will at least remind the public and politicians that some people do care about this.
Is any of this enough to affect change? Likely not. But it is a first step and if we can't even go demonstrate against this then we might as well stop caring. The possibility that demonstrations will not have the immediate effect we desire should not stop us.