Criticism of a Candidate's Positions on the Issues = "Dirty Stuff"?

John Weidner (Random Jottings) (hat tip: InstaPundit) soundly critiques Earl Ofari Hutchinson's "What Will Obama Do When There's No Hillary Firewall?". "Dirty stuff," to Hutchinson, seems to consist of, well, factually accurate criticisms of policy positions. Thus, Hutchinson writes,

There was an early hint of the dirty stuff that will come his way. The instant that Obama announced his campaign last February, National Rifle Association executive vice-president Wayne LaPierre wasted no words when asked about Obama's strong support for a ban on semi-automatic assault weapons, and severe limits on handgun purchases during his tenure in the Illinois Senate.

He called Obama's pro-gun control stance "bad politics." LaPierre's admonition was an ominous warning that the powerful gun-lobby group would oppose Obama, and so would millions of other passionate gun owners that take their cue from the NRA.

And that is "dirty stuff" because ...?