Salut Philippe -- I have seen many opinions on this subject, so you will get different answers, depending on who you ask and their perspective. Here are some examples:

The Civil Rights Project at Harvard University
http://www.law.harvard.edu/groups/civilrights/conferences/zero/zt_report2.html
Here's an article on zero tolerance from the magazine Mother Jones:
http://www.motherjones.com/prisons/investment.html
Another one from Britain in the Society Guardian:
http://society.guardian.co.uk/crimeandpunishment/story/0,8150,714678,00.html
A counter view by a California Republican who believes it does effectively prevent crime:
http://www.policyreview.org/nov96/backup/lungren.html
Zero tolerance in workplace drug prevention:
http://papers.nber.org/papers/W7383
Zero tolerance in schools:
http://www.ed.gov/databases/ERIC_Digests/ed451579.html
http://www.specialednews.com/behavior/behavnews/zerotolerance063000.html


On the Prevention Dividend Project website, we have collected a number of studies that look at the costs and benefits of crime prevention that you may also find of interest, including the International Center for the Prevention of Crime chapter that compares the costs of crime in different European and N. American countries:
http://www.prevention-dividend.com/en/research/justice.htm

California's New Three Strikes Law: Benefits, Costs, and Alternatives, 
RB-4009, 1994 - U.S.
http://www.rand.org/publications/RB/RB4009/RB4009.word.html

  RAND's study - a two-year effort by researchers at the nonprofit, nonpartisan research institute in Santa Monica, California - is the first to compare crime prevention programs with incarceration on the basis of cost and effectiveness at preventing future crimes. Researchers with the highly respected RAND institute found that, dollar for dollar, programs that encourage high-risk youth to finish school and stay out of trouble prevent five times as many crimes as stiff penalties imposed on repeat offenders with so-called three-strike laws.
  http://www.rand.org/publications/electronic/justice.html 



The Economic Benefits of Crime Prevention 
  Chapter 2 - The Economic Benefits of Crime Prevention includes data that show the costs of crime, the benefits of crime prevention and these costs compared to increased incarceration, jailing youth offenders and hiring more police officers. 
  http://www.crime-prevention-intl.org/english/prevention/chap2.htm 

Hope this is helpful... if you find any interesting economic studies on zero tolerance, I'd appreciate if you could share them with me for our website.
Thanks, Susan
Research Consultant
Prevention Dividend Project
www.prevention-dividend.com

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