According to a new report (PDF) from the Department of Homeland Security, drug offenders accounted for almost a third of the 128,345 "known criminal aliens" who were deported from the country in fiscal year 2009. The report does not specify types of drug offenses. But as I noted in a column last spring, noncitizens, including legal residents who have lived here most of their lives, can be locked up indefinitely and deported for extremely minor drug crimes. Selling a few grams of marijuana makes a resident deportable, and so does possession of drugs for personal use, including small amounts of marijuana in some cases. After "dangerous drugs," the second biggest category of crimes triggering deportation was "traffic offenses" (16 percent). The Drug War Chronicle notes that "persons convicted of what are commonly considered serious crimes (assault, larceny, burglary, robbery, fraud, sexual assault) made up only 20.7% of those deported."
Addendum: No matter how often I say that I am talking about people who live here legally, readers still respond by saying that illegal aliens have no business being in the country to begin with. If you enter the country illegally (or overstay a visa), you are already subject to removal. The issue here is people who live here legally until they become deportable because of trivial, often victimless crimes. What I'm suggesting is that lifetime banishment from a country where you have lived (legally!) for decades is excessively harsh for many of these offenses.