And, for the most part, the segment in BfC with Heston has been roundly criticized by both supporters and detractors of Moore. It was just overboard.
Even though Heston's Alzheimer's was not known at the time of the filming, it still came off as a petty and unfair attack.
That said, Heston was still acting as President of the NRA at the time, so he was certainly "fair game" for questioning...it just should have been handled with more finesse. Moore didn't do his otherwise powerful film any favors by badgering an old man.
So...yeah, not everyone who disagrees with Heston's stance on firearms is a "Moore" fanatic.