Well... this mob surely had protest as a reason (or at least a declared reason) to assemble and storm the building, so - yes, why not? There are other words tha

Well... this mob surely had protest as a reason (or at least a declared reason) to assemble and storm the building, so - yes, why not? There are other words that are applicable, but "protestor" is a semantically valid option. Unless by the "right word" you meant "how they should be called". But then it becomes a highly subjective question.