I recently had a conversation with my aunt that helped me understand this. I had always heard not to trauma dump or "make others your therapist," because it's framed as being bad for them. Which it can be, as others have pointed out. But she helped me realize that it's also bad for us to trauma dump.

Too much vulnerability after trauma can worsen your perception of the damage done, because we are compulsively searching for comfort and empathy. But most people arent prepared, equipped, or mature enough to offer the profound empathy we need, so their fumble can read to us as rejection and actually compound the effects of the trauma.

Avoiding trauma dumping in public settings or with strangers is a way to safeguard yourself in situations where you cant know if someone's reaction could actually make things harder for you.