Unintended consequence

Unintended consequences can be either

Examples of high scale unintended consequences

Of course, unintended consequences are common in everybody's life, but some can impact the whole society. Here are some examples:

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• In medicine unintended consequences are known as side effects. Most drugs have some side effects. As with other unintended consequences, these are often negative, but are sometimes beneficial; for instance aspirin, a pain reliever, can also help prevent heart attacks.
• The introduction of rabbits into Australia for sport led to an explosive growth in population, and led to rabbits becoming a major pest in Australia.
• "Prohibition", intended to suppress the alcohol trade, drove many small-time alcohol suppliers out of business, consolidating the hold of large-scale organized crime over the illegal alcohol industry.
• Sixty years later, the "War on Drugs", intended to suppress the illegal drug trade, has driven many small-time drugs dealers out of business, consolidating the hold of large-scale organized crime over the illegal drugs industry.
• The medieval policy of setting up large hunting reserves for the nobility has preserved green space throughout England.
• The wartime sinking of ships in shallow waters creates artificial coral reefs.
• In CIA jargon, "blowback" describes the phenomenon of supporting a foreign regime or terrorist entity, on the principle that your enemy's enemy is your friend, only to have it attack you, often with the weapons and resources you gave it. Examples include:
• US support of Colonel Manuel Noriega
• US support of the Mujaheddin in Afghanistan, most notably Osama bin Laden, and later the Taliban
• Numerous attempts by governments to reduce accommodation costs by the introduction of rent controls has led to the unintended consequences of shortage of property and reduction in quality or even the creation of slums — rental property not being built or maintained.
• Controversial research, carried out by John J. Donohue and Steven Levitt and published in the Quarterly Journal of Economics, suggests that legalized abortion accounts for as much as 50% of the drop in national crime rates. As evidence, they cite the fact that states which legalized abortion before Roe v. Wade saw drops in crime earlier, and that high-abortion states saw greater drops in crime than low-abortion states. Most convincingly, they found that, "in high abortion states, only arrests of those born after abortion legalization fall relative to low abortion states."
• Also controversially, it has been suggested that legalised abortion has led to fewer so-called 'crack babies'. The availability of abortion means that a drug addicted mother has the option to abort a fetus that her drug use is likely to render unhealthy (even if this consequence is not her priority).