There’s evidence that trigger warnings actually worsen anxiety and are counterproductive
The way to treat anxiety is to face the source of anxiety to try and change your relationship and reaction. The best way to do this is via controlled access that exposes one to the trigger gradually in a context that has no risk of harm (eg a media depiction, discussing the concept, building up to discussing the source of trauma that led to the phobic response if applicable)
Trigger warnings enable active avoidance. This sensitizes one to the aversive stimuli and makes the phobic response stronger. As a result when one encounters the stimulus (eg a friend, family, celebrity etc commits suicide, suffers an eating disorder, etc) your resilience to the trigger is now even lower and the response is more likely to be more significant than it was before.
That said education on access to resources like 988 or other warm lines can lower suicide rates, maybe. Research is more mixed here because it’s difficult to prove causation
https://journals.sagepub.com/doi/10.1177/2167702620921341 - the bigger takeaway from this one is that trigger warnings reinforce trauma as a central part of the traumatized individuals identity but they did find some incidence of drawback/harm
https://journals.sagepub.com/doi/10.1177/21677026231186625 meta finding no benefit and actually can cause an anticipatory reaction making the person more engaged with the material
There are others, this is just what grabbed from 30 seconds on google scholar. Its been a bit since I’ve done more serious lit review and it’s not like I keep a directory of papers I’ve read
The issue is the culture surrounding trigger warnings. Let’s be real here, people looking for trigger warnings are generally (perhaps overwhelmingly) not looking for material to help with their exposure therapy. They are looking for a “warning” to help them screen material to avoid. The issue is that this creates an unrealistic expectation that is incompatible with the real world. You can avoid suicide, sexual assault, eating disorders, or whatever in your media (maybe) but real life won’t sanitize itself or warn you. You will encounter these topics, whether through the news, careless speech from friends, or even intrusive thoughts of your own. Research continues to show that avoidance of upsetting topics can worsen anxiety and ptsd symptoms
To your final point the idea of it helping to create a choice isn’t even as clear cut as you describe
https://journals.sagepub.com/doi/10.1177/21677026221097618 content warnings actually increase the likelihood someone will view problematic content. This point is further reinforced by similar findings in the meta linked above
So you have a system that ultimately makes creators feel like they’re doing something noble, that is likely at best useless and potentially harmful. Said system increases the likelihood that a person will view the problematic content but also enables the reality that a person will simply avoid the things that provoke their anxiety which again is more strongly established as harmful
https://www.sciencedirect.com/science/article/abs/pii/S0005796712001064 - ptsd worsens with avoidance
https://www.sciencedirect.com/science/article/abs/pii/S0962184904000290 - anxiety disorders do the same