Groupthink

A person is smart. People are dumb, panicky, dangerous animals and you know it.

Groupthink (or communal reinforcement) happens when a desire for conformity within a group transcends rational thought, issues of right and wrong, or even personal opinion. When this happens, individuals in a group fail to express their doubts as commonly about the group's dynamic, direction or decisions because of a desire to maintain (pseudo-)consensus or conformity. Thus even though the group may be on a headlong rush to error or disaster, no-one speaks up because they don't want to rock the boat.

Groupthink can affect communities of any size from small groups to whole nations.

Origin
A group's members tend to ignore or not voice their own doubts "for the good of the group". The group itself may also ignore external suggestions, and can become paranoid when faced with heresy or with criticism, even when the criticism is helpful or even just well-meant. Within a group, repeated assertion may lead to members accepting dubious claims uncritically without  proper research or empirical support.

Groups are most vulnerable to the results of groupthink when their members come from similar backgrounds, when the group is insulated from outside opinions, and when there are no clear rules for decision-making. Alternatively, in the case of destructive cults, a clear rule may exist: "Accept what the cult leader or the leader's representatives tell us without question - otherwise face the consequences."

The famous social psychologist Irving Janis popularized the word "groupthink" in 1972; the term itself originated with William H. Whyte of Fortune Magazine in 1952. Groupthink relates in some ways to the older concept of crowd psychology, although "groupthink" refers not to the spontaneous actions of crowds but to the activities of groups with a shared interest or objective (such as LGATs ), including many small groups, and groups of people who may be physically distanced from each other (for example, people in an Internet community). The similarity of the term to "doublethink" may suggest that Orwell's Nineteen Eighty Four inspired the naming convention.

"Groupthink" is why everyone in that online forum/wiki you just joined not only doesn't go for your perspicacious and radical ideas, they actually seem uninterested. Sheeple!

Role of the iconoclast
For if you kill me you will not easily find another like me, who, if I may use such a ludicrous figure of speech, am a sort of gadfly, given to the state by the God; and the state is like a great and noble steed who is tardy in his motions owing to his very size, and requires to be stirred into life. I am that gadfly which God has given the state and all day long and in all places am always fastening upon you, arousing and persuading and reproaching you.

A community's "drift" can seem to be automatic. This drift is frequently kept in check by an iconoclast who may seek to redefine that which has come to be defined precisely because of the group's drift. This serves to shock the group out of the automatic "go with the flow" and the more insidious "go along to get along" attitudes which can eventually get in the way of the group's stated goals.

Sometimes iconoclasts, other than actually supporting or protesting something which is wrong and/or incorrect, are just bigoted jerks.

A more proper term for someone who challenges ideas for actual philosophical purposes is a "social gadfly" which is how Socrates referred to himself during his trial for "corrupting the youth" and "impiety."

Epistemic closure
Julian Sanchez of the Cato Institute adapted the term "epistemic closure," originally to describe what he saw as the behavior of US conservatism. In a blog post that kicked off the "epistemic closure" debate of 2010, which drew in Andrew Sullivan, Jonah Goldberg, David Frum, Ross Douthat, Bruce Bartlett, and Jonathan Chait, Sanchez wrote:

Reality is defined by a multimedia array of interconnected and cross promoting conservative blogs, radio programs, magazines, and of course, Fox News. Whatever conflicts with that reality can be dismissed out of hand because it comes from the liberal media, and is therefore ipso facto not to be trusted. (How do you know they’re liberal? Well, they disagree with the conservative media!) This epistemic closure...

His usage is close to "false consensus" or "groupthink."