One of the problems with a democratic form of governance is that the dissenting opinion requires to be backed up by law of numbers. That is, if you are comprising of the minority and have an opinion, then the majority's opinion is thrust upon you.
|"Death of Socrates", Oil on canvas painting by Jacques-Louis David (1787)|
So what do you do when you dissent against the majority. Revolution and coups, though a solution, are not to be espoused, as any violence(be physical or psychological) removes the sanctity of the system and causes further degradation.
Rather, holding onto the dissent and working on establishing the dissent with valid evidences, prototypes or a fully-fledged working solution would be a constructive form. We often see that dissents are often restricted to opinions alone, and are not followed up with the scientific rigour to productize the opinion. If you are a change-seeking-agent or an activist, rather than cribbing, complaining, shouting or holding the placards, getting to the crowd and sowing the seeds for the change would be a constructive form.
And if you are still not heard, then use the placards to showcase the solution.
And if you are still not heard, move on.
Contrary to the idea of dissent in democratic forms, in some organizations, there is a general principle of HIPPO - i.e, Highly Paid Person's Opinion :)