Group members sometimes fail to consider a range of viewpoints and alternatives in an effort to maintain cohesiveness and a "united front." this is called:

I believe this is called Groupthink.
Groupthink will make members of a certain social group feels the pressure to hold on to a certain value/principles in the fear of being outcasted as a pariah.
Because of this, it is really hard to introduce a differing value/opinion to this type of groups.