To me, the absence of a military draft is the most important factor behind the minimal number of violent protests against the increasingly unpopular war in Iraq. Explicit riots over the draft already occurred in New York City during the Civil War soon after the North instituted the draft in 1863. These riots were mainly by young working class men who could not afford to buy a substitute, a system in effect at that time. So it is no stretch to claim that violent riots have occurred in the United States when unpopular wars are combined with a draft.
Recall that President Nixon and many other politicians during the Vietnam War felt that the drafting of young men to serve in the armed forces was partly responsible for the violent protests against the war. As a result, Nixon in 1969 set up the 15 members Commission on an All-Volunteer armed Force (Gates Commission) to look into whether an all-volunteer armed forces should replace the draft. Milton Friedman, Alan Greenspan, and General William Westmoreland, who had commanded military forces in Vietnam until mid-1968, were all members of the Commission. Apparently largely due to the persuasive powers of Friedman, the Commission, while initially evenly divided between those in favor of and those opposed to the draft, came out in 1970 with a unanimous recommendation to end the draft. The draft was abolished in 1973, and protests largely vanished, although the war did not end until 1975.
Representative Charles Rangel of New York has proposed to reinstate the draft. He has claimed that President Bush would not have invaded Iraq had a universal draft been in place. I do not believe he is right, but I do believe the pressure to withdraw earlier would have been far greater if young men were being drafted in large numbers.
The war in Iraq is being fought only with volunteers for military and civilian service, although some members of the armed forces and the reserves would not have joined if they anticipated the war when they enlisted. The reliance solely on military volunteers means that "taxes" to fight the war are spread over all taxpayers, and are not concentrated on young people. Moreover, draftees are more costly in terms of the resources lost to other activities, and they are on the average less dedicated to the military than are volunteers.
When draftees, and those who volunteer mainly to escape the draft, make up a significant fraction of military personnel, much of the burden of a war falls on them, not on the average taxpayer. Even those who volunteered during the current war have shifted some of the burden of their service to taxpayers by demanding and receiving higher pay. Since most of those involved in violent protests in general, and wars in particular, are usually young males, is it any surprise that they are protesting much less during this war when they are paying a much smaller share of the cost than young men did during Vietnam?
I agree with Posner that the many fewer deaths from the Iraq war than from the Vietnam War have weakened the impetus to protest violently, despite the war's unpopularity, although the slightly over 3000 deaths have to be augmented by the many more serious injuries to military personnel to get a full measure of the personal cost of the war in Iraq (see my discussion of the cost of the Iraq war in the post on March 19, 2006). Still, I believe violent opposition to the war would have been far greater if many of those killed or seriously wounded had been draftees, .
My emphasis on the importance of the draft in sparking unrest during the Vietnam War may seem misplaced since most young men who took part in violent protests were college students. Until 1969 students usually had their military service deferred. However, students could anticipate being drafted when their education ended. Studies have shown that the number of students in colleges and universities expanded during the Vietnam War beyond the numbers expected in peacetime because some persons continued with their education only in order to escape, or delay, being drafted. Even if college students ended up avoiding the draft, they were being indirectly taxed if they only stayed in college to avoid that. They would have been attracted to protests in recognition of the indirect costs they were paying as a result of the draft.
An additional factor that encouraged protests by college students during the Vietnam era is that the returns to college were not high and were declining then for the typical student, not only for those in college to avoid the draft. The major change in this regard during the past 30 years has been the unprecedented increase in the monetary and other benefits of a college education (see my post on April 22). Since the 1970's, real earnings of young high school graduates hardly increased, if they did at all, while real earnings of high school graduates increased slowly. The only explosion in earnings has been among college graduates, especially of younger ones. With no risks of being drafted, and with a potentially large cost from reduced job opportunities if arrested for participating in violent protests, college students could lose a lot more now than during the Vietnam era by joining such protests.