The rebellious people are the ones who change society. They are very important because they make all of of changes happen. Without them there would be no progress;we'd be the same. Some of them are welcomed; some are shunned from society. Either way, the rebellious amongst us -even if we don't agree with them- are essential to the world.
It depends on the situation. Sometimes change is justifiable, as in limiting working hours to eight hours a day and requiring overtime pay beyond that limit, and giving women the right to vote. Changes that were not justifiable were allowing insurance companies to become for-profit enterprises, and permitting corporations to raid workers' pension funds and steal money that workers had put into the fund for their retirement.
This question begs a question in response. Behind what? It really boils down to to an individual and their ideology. As chestnutrules pointed out, when an individual has a progressive ideology - then yes, society is always behind and the natural progressive while always push for change - for the sake of change and it can't happen quickly enough to appease this attitude. For the radical (extreme progressive) the change is never enough. It is in this spirit they are rebellious by nature.
However, a person who is conservative probably does not believe society is behind as you put it. They typically wish to conserve (conservation) ergo conservative culture . They like things as they are and do not wish to have the world they live in to be constantly changing and react to this change ergo the term reactionary conservative. The fight to keep things as they are.
Most people today live somewhere in between this spectrum. They agree some change is needed and recognize the value of maintaining continuity and cultural value. The truth is - both conservatives and progressives compliment each other. It is important that society maintains a parity between these two ideas because without one or the other this house of cards would come crumbling down as it always has done.
The question one should really ask themselves is, should law dictate culture or should culture dictate law? It is a tough question to answer when you really think about it from both perspectives.