I don't think you know what you are talking about. The original use of "trigger warning" was very specifically intended for use on graphic material that could trigger a dissociative episode, for example an explicit description of child abuse or rape.

The phenomenon you are referring to - appropriating the language of PTSD for concerns of politics, taste or personal offence - is exactly why some people advocate replacing "trigger warning" with "content warning" or similar (and not because of associations with gun violence, as OP asserted).