This is not a point for using it for something that the majority of people posting in the thread already know.
If spreading spoilers hurts then its hurt is not limited to vulnerable people posting in the thread, but encompasses all vulnerable people reading the thread.
The context of this post was “rot13” vs “a proper collapsing or color-based spoiler tag to be implemented in markdown”, so this is not sufficient to make difficulty a point in rot13′s favor, even if it ever was. The people who don’t want to read spoilers don’t have to view them, in the case of a spoiler tag. Choosing a spoiler tag over rot13 only harms people who A) are harmed by seeing a spoiler [and do not already know the spoiler] and B) have enough willpower to resist un-rot13ing it, but not enough to avoid selecting the text to view it without an external program. That sounds like a very tiny group.
The context of this post was “rot13” vs “a proper collapsing or color-based spoiler tag to be implemented in markdown”, so this is not sufficient to make difficulty a point in rot13′s favor, even if it ever was. The people who don’t want to read spoilers don’t have to view them, in the case of a spoiler tag. Choosing a spoiler tag over rot13 only harms people who A) are harmed by seeing a spoiler [and do not already know the spoiler] and B) have enough willpower to resist un-rot13ing it, but not enough to avoid selecting the text to view it without an external program. That sounds like a very tiny group.