I think you are reading too much into KOTH being liberal. Remember the episode where Bobby and Hank entered the shooting competition? Hank is not a good shooter and hates to admit it. Peggy embarassed at Hank says "Hank, guns are what keeps this family together."
In another episode Cotton (Hanks dad) teaches his newborn son to shoot a gun. It's funny in that context.
Also Cotton gets Bobby a Winchester 20ga shotgun for his birthday on one of the earlier episodes.
Yeah they have some digs at guns, like they dig at EVERYTHING, but I don't think it's in an anti-gun way.
Also, Mike Judge and Greg Daniels created KOTH. Judge created Beavis and Butthead, Daniels worked on the Simpsons.