@KenBrenner for me it's the crowding at the shelters and the an obvious sub-culture of folks who want to (IMO) be some sort of AT resident, searching for words here.
The party atmosphere, e.g. 'trail days' in Damascus gets a little ridiculous. (funny, I sound like the 'get off my lawn' guy)
It seems to me, from my observation, that many if not most folks start as 'backpackers', but somewhere along the line, the whole thing for many becomes some sort of moving fraternity party.
AND, at every shelter, there is some really old grizzled thru-hiker guy (or says he is), very nice, but is more than willing to 'share his wisdom'. (reminds me as I write this of the guys that dress up like Roman soldiers at the Colosseum...."get your picture taken with a real life 'thru-hiker'").
I do a lot of 'section hiking' along the AT's longest corridor (tree tunnel?) here in VA and these 'caricatures' never seem to change.
Although the AT is convenient, I always recommend to folks, get out of the tree tunnel, go hike the PCT or CDT.
It's like Mark Twain noticing certain patterns of characters along the Mississippi