I just want to add something as someone who has volunteered a lot for the local AMC Bostson committees.
There's a HUGE difference between what I called "corporate" AMC and the local chapters/committees. Please don't mix them up. Corporate AMC is what you see in the glossy magazines and have trips, hotels and classes that charges a lot of money. I have not much to say about that.
Then you have the local chapters in Boston, NH, CT etc and each chapter have local committees for climbing, hiking, biking etc. Each committee is totally independent from any other committee and chapter. They don't even know what others are doing and are purely run by volunteers without any pay.
So when you meet an AMC group, its very important to know if its a corporate group or a local committee as its' very different and you cannot lump they all into one group. Again, each committee is an entirely different entity from another committee. If you see one group behave a certain way, it has nothing to do with another group. They may as well be a group called XYZ. They just happen to have the same three letters at the front.
As someone who led many climbing and hiking trips for local Boston committees I would say that most leaders (if not all) in our committees are very accommodating with people outside the group. There is no such thing as "ours". Sometimes, yes, the group for the location got big, but we always tried accommodate other parties. We also continuously have discussed among us how to make that smoother and really respect other people as the locations is for everyone.
We also focus on teaching people about the outdoors and what proper behavior and etiquette is out on the cliff and mountains. As someone who didn't know any climbers before I started climbing with AMC Boston, I thought I learned a lot from the people there about being respectfully for others, about the nature, mountains and the area.
Please don't lump all of AMC all together and when you find an issue, find out which committee had the trip and contact their chair. They will most likely take the issue seriously and take care of it. I know the local Boston committees always do that.