Is his participation in the Second Amendment March going to help or hurt ?
At face value, it will help. He has a large organization, and has name recognition. On the other hand, those that are not FUDDS, weekend warriors, and tend to stay "in the know", it may hurt credibility. But not at the March, that is a bigger issue that transcends Piazza...
The Second Amend March is a GOOD thing. I can't do the NRA convention, AND the March, but promoting a March in DC that reminds the "Beltway Folks" that the 2nd Amend WILL remain as written, is a good thing.
If Piazza brings assets that promote the 2nd Amend; Fine. If he utilizes different marketing and salesman like tactics to sell his own product, than over time most folks will catch on, and he will just be "Oh, that guy"....