Janis’s theory about group thinking is extremely interesting. My main takeaway from the given excerpt of his book is that group thinking is a reference
“…to the mode of thinking that persons engage in when concurrence-seeking becomes so dominant in a cohesive group that it tends to override realistic appraisal of alternative courses of action”.
When applying the theory to normal day to day situations it becomes clear that this is something that happens often and most commonly through subliminal peer pressure. Though it may not be explicit, peer pressure, as suggested by Janis, occurs when a group is attempting to concur on a topic/decision, so if members of the group are steadfast on a decision, whether because they agree with it or because they too are a victim to the pressure, it discourages any alternative suggestions.
This becomes problematic when considering the consequence of being reluctant to change/alternative actions. Janis addresses one of the most prominent and harmful results of group thinking when he mentions war strategies. Often times military leaders will resort to mass killing, mostly civilians, in order to convince foreign governments to cooperate. Though there are other options there’s a tendency to kill because that has been the unspoken and reigning consensus, so much so that people hesitate to even offer different methods.
Group thinking, in the absence of all the context provided by Janis, seems effective in that it produces quick decisions, however, a deeper analysis of the term makes it clear that while effective, it is also both detrimental to progression and unethical.
I think your comment about group consensus leading to killing masses of people. When groupthink occurs it leads to a stronger in-group community which makes the opposition or enemy seem even more like outsiders than they may be. With this logic, it is easier to create large massacres and use more violence.