I was looking through A Dictionary of Basic Japanese Grammar recently and found this as an example under
Kazuo's friend read his (= Kazuo's) letter (and Kazuo was unhappy).
And another under
Lit. I got my cake eaten by my younger brother. (= My younger brother ate my cake (and I was unhappy).)
I found this to be a bit strange, because I can't see why the subjects necessarily become unhappy even if the events were not of their control.
After looking around a bit, it appears some categorise one of the uses of ～られる as a "suffering passive" form, with some adverse implication for the subject unto which the action has been performed.
However there are others that say that such a thing doesn't really exist and that it's context specific. This is also explained partially in the Dictionary under
rareru (1), note 7.
What connotations are there with ～られる? And are there ways to discern them without the use of context?
There has been an almost identical question posed on Reddit, but I feel that the answers didn't really explain where this general view comes from.