Scientific consensus, is a broadbased agreement about a scientific theory.
But in the context of political debates, scientific consensus for a theory has frequently been claimed without regard to whether there is any actual scientific evidence for or against it. The claim is then used by powerful political forces to completely shut down any and all dissent from select theories and to prevent alternate theories from being researched or even simply presented.
- "Science, in the public arena, is commonly used as a source of authority with which to bludgeon political opponents and propagandize uninformed citizens. ... It is a reprehensible practice that corrodes our ability to make rational decisions." 
- "Essentially if whatever you are told is alleged to be supported by 'all scientists,' you don't have to understand [the issue] anymore. You simply go back to treating it as a matter of religious belief." 
It was still the scientific consensus when Darwin wrote Origin of the Species in 1859 that microbes arose by spontaneous generation.