The 'experts' at Britannica blog commit another howler... here's my response (awaiting moderation).
Goodness, if you’re going to attempt to use logic to make your point, at least avoid uncharitably confusing an inductive inference with a categorical syllogism.
Sullivan is obviously making an inductive inference. He is inferring from, “I have seen thousands of gang members and none of them have been incarcerated for possession” to “gang members are not generally incarcerated for possession.”
It’s the same form as “I have seen thousands of rabbits and none of them were pink, thus, rabbits are not pink.” It does *not* assume that “Only those rabbits which I have personally witnessed actually exist.”
The appeal to an implicit premise (it’s called a ’sorite’) is common and can, indeed, lead to fallacies (see ‘The sorites paradox’ http://plato.stanford.edu/entries/sorites-paradox/ ). This is not one of them. This is pure and simple logical blundering, or what we would call in philosophical circles, a howler.
For more on logical fallacies (real logical fallacies, not the fake one described here) you can see my http://www.fallacies.ca