I am not entirely sure how well some of the inspiration jives with the questions, for a big reason: a lot of what's being complained about, from the summary provided, is about wish fulfillment and people's wishes being not granted. That's a different animal by far than being shocked and surprised by the appearance of unexpectedly traumatic and highly personal subject matter that might set off somebody's PTSD or somesuch.
The former is not getting the pony you asked for when you were five. The latter is unexpectedly getting the pony you had when you were five served to you for dinner without warning, and those two things are in no way the same.
1a (players): It's a player's responsibility to be as aware as possible of their own limits and boundaries. This is possible only to a point, however. Someone may never have been exposed to <subject> before, and may not know until then that they find it troubling or disturbing to them. It may also be simply a matter of how something's played out. Taking a film example and comparing it to RP doesn't always work, because there is a greater measure of separation in material you're passively consuming vs. that with which you're interacting. I can watch a rape scene in a film and only rarely has it bothered me (exception: Strange Days, which is a great movie, but holy shit did I have to stop watching it the first time after realizing what the hell was happening). I will not go within a mile of one on a game.
That passive vs. interactive difference is huge, because while both are works of fiction, you are actively engaged with one in ways you are not with the other; that alone diminishes the separation factor. You, the player, are involved, even if the events are occurring to a character in the story. There's less separation in RP by default here.
1b (storytellers/GMs): If you know you're including something that is a common trigger, label that shit up front to enable people to make the decision for themselves as to whether or not they wish to participate. If they read the warning and ignore it, it's on them. People should be given the tools to make an educated choice, however, and there are no two ways about this one to me: this is a fundamental and genuinely baseline level of player-to-player respect in my book.
1c (game): Games should set clear standards re: the maturity level expected on their game, which subjects they will allow, and which they will disallow (if any), and whatever other conditions apply. If something about the setting or game world is commonly objectionable (sexism or slavery in historical settings, religious persecution, etc.), even if it should arguably be understood that players should know this coming in, you should still lay out how this is handled on your game. Is it minimized? Not a thing? Handwaved away? In full force IC? In full force IC for NPCs but players are exceptions? "It happens, it just doesn't happen right here... " -- whatever you're going with, say so, and say so clearly. If something requires additional approvals to go into it, say so. If anything goes, say so.
(Other two post-nap.)