Social Norms are indeed massively subjective. Then again, morality is the will of the masses. What is wrong and what is right is determined from the environment, not the subjects. If we for example were on a war with aliens our current morality wouldn't change. If Dinosaurs roamed the earth along with us it would be a different st of rules.
I am not saying that this is what make it "right" but rather how things will always will be.
A consequentialist would say the consequences of any action is what ultimately determines if it was correct or incorrect. This of course is very rational. Most people don't make their decisions rationally, and the irrational far out number the rational. A rational person would simply see risks and benefits, and some protests are more risk than they are worth in benefit.