These days, revisionists are viewed as people who push a wrong view of history for the sake of a political agenda. However, that's not really what it'

Historical revisionists are people who challenge the mainstream view of a particular point in history. This isn't inherently bad. If new information contradicts the orthodox viewpoint, maybe that viewpoint should be revised. If you believe that the Soviet Union wasn't that bad, the American Civil War was about more than just slavery, or that the Gilded Age wasn't so bad because the economy was growing very fast and all the problems attributed to it weren't new, congratulations, you're a revisionist.

Granted, there are some forms of revisionism which are wrong such as Holocaust denial. However, revisionism itself isn't a bad thing, pseudohistory is. Pseudohistory can be done for several reasons. Sometimes, it's tied to a conspiracy theory such as the pyramids being built by aliens. It can also be done for political (and perhaps more than often than not, for racist reasons). This would include many theories about the Jewish people, genocide denial in general, and that slavery wasn't that bad.