This rhetorical fallacy is better known as argumentum ad populum. What it means, in layman's terms is "everybody knows X is true."
Examples the Left loves to trumpet:
- Everybody knows man-made Global Warming is a fact.
- Evolution isn't just a theory, it's a fact. There are no legitimate alternative theories.
Actually, neither are proven facts. Yes, there is widespread belief in both, largely due to the fact that they are taught unopposed in schools and due to significant Group Think amongst the scientific communities who support both.
For the record, I am not a scientist, nor do I have any intention in engaging in a debate on either topic. They are simply not my area of expertise, and to attempt to argue for them would do nothing but set back those who have studied them in their goal of entering into a legitimate discussion on the topic. (So don't try to debate them with me in the comments or on the Biblical Conservatism Facebook page. I'm not going to do it. I'm no more qualified to argue these points than President Obama is to argue Economics, and unlike the POTUS I'm wise enough to recognize my shortcomings. Offense intended.)
Any questioning of these ideas is met with ridicule from their colleagues. Ask Michael Behe.
When Behe began to argue his Theory of Irreducible Complexity the Biology community, specifically the Evolutionist wing, began to jump down his throat and pile on against him. Combining that piling on with Appeal to Ridicule and you have many other members of the scientific community refusing to even consider the potential validity of Behe's argument.
The scientific response would be to conduct opposing experiments in an attempt to disprove Irreducible Complexity by demonstrating that the cells that Behe argues are irreducibly complex could in fact be functional at a lower level of complexity. Instead we get ridiculing of those who dare to question the Group Think.
Furthermore, true science should always be called to perpetually question it's own findings. The two above branches of Biology (Evolutionary Biology and Climatology) have shown a complete lack of desire to question their current positions. Instead of doing what most other branches of science do (continuing to perform experiments to check the validity of their current hypothesizes) they instead continue to argue that everyone agrees, therefore they can simply conduct experiments to further prove the existing "fact."
There are political implications as well. As most uniformed voters: "Everybody knows that Democrats are more compassionate than Republicans." (This is both a great example of a political meme and of the Neighborhood Liberal trap of compassionate intentions with no concern for results.
The bottom line is this: Consensus is neither science nor reality. It simply means it's either been repeated several times or group think has set in. Don't accept (and therefore be silenced by) consensus.