Steel, I am from MA, so I understand the process and what a pain it is. My chief tried to talk me down to a Class B, but I persisted for a Class A ALP. I would list the following reasons for wanting a Class A:
-You want to be able to buy and own high capacity magazines.
-You want to be able to buy and own handguns and rifles that will accept high capacity magazines (this is crucial, as with a Class B license, you cannot buy any gun that could accept a hicap)
For the "All lawful purposes" clause, I would say that "you want to be able to carry a firearm for personal protection should you wish." I like that language because 1) it is entirely within your right to want to do so, and perfectly reasonable and justifiable in the eyes of the law, and 2) it does not directly allude to a problem with crime in the Chief's jurisdiction.
I was told in my Safety Class that if you are denied your permit, you have the right to appeal. The chief must then explain why he has seen fit to deny you the right to carry. That he doesn't give out permits or that he doesn't like you are not valid reasons. I also hear that a letter from an attorney stating as much often changes their stance as well.
I would contact GOAL, at goal.org. They are fantastic and very helpful for the licensing process.