If we accept it as a norm there's nothing more stopping them. You can't point at one and push him/her out of politics, when it's a broadly shared assumption they all lie equally. If the cynical position becomes the norm, all trust is obliterated and the society becomes dysfunctional, unable to expect any standards, expectations of positive outcomes. This is to the benefit of the particularly cynical and corrupt in power, it is very much against the society. It also blocks any chances for a self-organised response, as instantly anyone who becomes a leader in any noticeable way, or simply a speaker for any concept or vision is expected to be as corrupt, and so there's no chance for creating or promoting an alternative.