Having a frank and vulnerable discussion of your trauma with someone you have emotional intimacy and trust with is incredibly important and can help the healing process. I'd highly encourage people to do that.
However, I think the term "trauma dumping" often refers to the practice of sharing your trauma with people who you don't have a close relationship with, or with people who you haven't interacted with long enough to generate trust.
I am a former trauma dumper, and I dumped my trauma all over a person who I should not have. That person turned out to be a very untrustworthy person. Their knowledge of my wounds allowed them to do some incredibly harmful things to me over the course of an eleven months relationship. I managed to escape, but it was a bad move, and I learned to become more careful about who I shared that information with.
Plus, there is always more to you than your trauma. It certainly doesn't feel that way when you're really stuck in it. Hell, me saying that may have just made some people very, very angry. I got really angry when my therapist said that to me, because it felt like she was minimizing what I went through.
I came to understand that she meant I was an adult with passions and a whole life, and that adult is what I should share with people. By letting my adult self live in the present, I became more able to take care of my trauma using the inner child metaphor. My wounded inner child is precious and deserves care, and I share that with people who will appreciate that. The adult that I am also deserves to live and see the world, and deserves to be recognized by friends and family. Trauma dumping inverts that.
People stop getting to see the awesome person you grew into because humans are wired to pay attention to wounded children, be they physical or metaphorical. Some people will be tender, some will be dismissive, and a few people will take advantage.
So yeah, please share your trauma when it makes sense to, with people you love and trust. If there's a mutual understanding, then any sadness they feel will likely be offset by the warm knowledge that they've helped you make it through another day and maybe heal a bit more. That's what is shown in this meme. Let your adult self live your life the rest of the time, and use that adult to give the kid the care they needed but didn't get.
(Wow, now that I'm rereading this post, I feel a strong sense of irony. Like, it's not a trauma dump, but also nobody asked for me to write a fucking essay about a meme lol)
Yep, sharing your trauma should be an exercise in trust and intimacy. People should not share their trauma with others just to provoke a specific emotional reaction. I also have some second-hand experience with what you mention. One of my SO's parents is a hideously narcissistic person who would trauma dump all over my SO to invalidate any feelings or concerns my SO might have. That, combined with gaslighting and other forms of emotional abuse and neglect, plus some physical and sexual abuse set my SO up with a fuckton of trauma to process. They also had a hard time with hearing of other people's traumas, although for them it was in more specific circumstances, rather than generally.
I like to think that most people trauma dumping are victims who aren't creating another iteration of the victim/abuser cycle (I base that off of nothing but my own hopes, I have no numbers), but there are definitely people who have weaponized it. I'm sorry to hear that you went through that :/ hopefully you're free from those toxic people. After my SO's parent kicked my SO out (a horrible night, but one of the best nights of their life in retrospect), my SO moved in with me, did a whole lot of EMDR therapy, and has managed to heal from the damage caused by their parent. Hopefully you can find a treatment, process, or mindstate to help you, since it sounds like you still have some wounds from what was done to you.