What are your thoughts on "trigger warnings?"?

A trigger warning is when you warn potential readers that something that you’re writing will contain disturbing content so that they can avoid reading it if they think they will be bothered. The idea is that being reminded of certain topics can “trigger” a PTSD flashback.

Trigger warnings are becoming increasingly supported online to the point that people will often be criticized for not including trigger warnings if they write disturbing content. This is making some people angry or annoyed with the entire concept. Their argument is that people can’t be made responsible for others’ sensitivities.

What do you think of trigger warnings? Are they helpful? Are they overused? Should they be a part of general social etiquette? Should we expect people worry about other people’s sensitivity when they write content on the internet?