"Zero tolerance" is a popular buzzword among polyticians and other demagogues. Most of the opinion leaders who throw around zero tolerance rhetoric are smart enough to realize that 100% abolition of any phenomenon is generally impossible. More often than not, it's even theoretically impossible! Nonzero tolerance may also be useful in avoiding "divide by zero" errors. Last time I was at the library (i.e. last time I accessed the internet) I was browsing Wikipedia, where I found a reference to "zero tolerance" in the article on Discordianism, of all things.