“The people can always be brought to the bidding of the leaders. That is easy. All you have to do is tell them they are being attacked and denounce the pacifists for lack of patriotism and endangering the country.”
Basically, people will fall in line if a) they are scared and b) they are worried they could lose the support of their communities by disagreeing. Building off of this intuition, psychologists have found that when people think about death, their adherence to in-group ideologies increases (Navarette et al., 2004). My guess is that accusing dissenters of lacking patriotism in promoting wars is effective in part because it questions loyalty to the group and references a potential threat. No one wants to risk losing their ties to the group when times are dangerous.

p.s. the quote is from Herman Goering, one of the Nazi officers Gustave Gilbert interviewed at Nuremberg. Check out Gilbert’s book “Nuremberg Diary” for more.

http://www.amazon.com/Nuremberg-Diary-G-M-Gilbert/dp/0306806614

Navarette, C., Kurzban, R., Fessler, D., & Kirkpatrick, L. (2004). Anxiety and Intergroup Bias: Terror Management or Coalitional Psychology? Group Processes and Intergroup Relations, 7, 370-397.