I am glad that I retired before the subject of trigger warnings became a major topic of conversation in higher education, and even gladder that it would have been close to irrelevant in most economics classes (the exception, for me, probably, being when I taught US economic history and had to deal with slavery). This article at VOX is a fairly helpful introduction if you haven't had any occasion to follow the issue.
I have always argued that one of the things I valued in college, and that I think is one of the most valuable parts of attending college, is the opportunity to encounter different points of view, and provocative issues and opinions, in a safe environment. Note that there are two parts of this--the encounter with ideas that may make you uncomfortable and the safety of the environment in which you encounter them. My feeling about warnings on syllabi (etc.) is not that they give students to opt out of difficult, challenging, provocative, or uncomfortable material, but that they are an effort to help prepare a safe place to encounter all those things.
In some cases, a faculty member may have to go beyond a warning, and discuss, either on the syllabus, or in a handout or in a video or in a one-on-one session with a student, what the purpose of the material is. It may require thinking about how one presents the material (the discussion of Ovid in the VOX piece suggests to me that perhaps a consideration of how one approaches the material is worth while; the same may be true of some images in art history)--not to avoid the material, but to place it in a context that makes students feel safer (while still being challenged) with (by) the material.