Joe the plumber,or any plumber, does not need a license unless they are a contractor or own the business. These people know that but they are trying their best to make this guy out to be a jerk. It is working, they are merely going to piss off a bunch of working class people.
and that smear will work with many people.
As the old saying goes, "If you throw enough mud, some of that mud WILL stick, and the mud that DOES stick,,,
is very, very, very hard to remove."