South Park almost always is preachy, though this episode went over the top -- on purpose -- with the preachiness.
Parker and Stone (the creators of South Park) were very upset over the censorship issue, especially given recent events around a few of their episodes -- most specifically, Comedy Central apparently caving into pressure to pull the 'Tom Cruise is in the Closet' episode that poked fun of Tom Cruise and Scientology/Scientologists in general.
This episode was also clearly pointing out the idiocy of giving into demands and pressures over publishing cartoon images of the Islamic Prophet Muhammed (sp?) because of fears of riots like were seen in Europe.
Preachy yes, humorous yes, sadly ironic yes.