Poor Jason
Watched this documentary recently, and was surprised by how openly Jason was treated as a second rate citizen by the other band members. I've read some interviews, including the one in Playboy from back in 2001 or so, where Jason relayed some of the mistreatment he received, and in this documentary there's plenty for us laid bare to see.
It's most noticeable in the second part, the one documenting the tour. For example, after the first show when James tells Jason that he's messing up the backing vocals on Master of Puppets, or later when the band is doing interviews backstage at the Freddie Mercury tribute, and James yells for Jason "Hey d!ck, get over here", and then says to Lars and Kirk something like "(Jason) seems to think just because we turned his bass up on the record he can make us wait" (I don't remember the exact quote). Kirk made fun of Jason when he pointed out that Jason takes sandwiches made with backstage catering back to the hotel after shows so not to spend money on room service (which I found to be rather sensible and even endearing on the part of Jason).
I love Metallica and think James is a creative genius and that Lars is a business/promotional genius, and Kirk is an underrated guitarist, but there's no doubt that they treated Jason rather poorly. A short-term hazing period is understandable, but clearly as late as 1992, five plus years after Jason joined the band, they were still at it.