I have been through 11 years of infertility. I have never been pregnant, but I have two children through adoption. The first we waited 7 years for, and the second took 3 years of actively pursuing both ttc and adoption.
I think that it is so important to be allowed to have those "ugly" feelings. I spent years having people tell me how everything I was feeling was wrong. If I expressed that it was hard to see a pregnant woman or go to a baby shower, I got told that I needed to learn to be happy for other people. I had all this grief and anger inside me and no place for it to go, because every time I attempted to express even a tiny part of it, I got informed of how my feelings were not valid and I "shouldn't" feel that way. Well, feelings are not always rational, especially when we're grieving. I think it's important to be able to express those feelings somehow. I do think it's also important to be careful where, when, and how we express them, because when we are angry, it is so easy for someone else to be on the receiving end of our feelings. I also think it's important to acknowledge to ourselves that our own feelings may be irrational. They're still real, but they don't necessarily reflect the way the world is or the way it should be.
I also think it's important to recognize that whenever we feel unfair about someone else having something we want or claiming an experience as their own, someone else might be feeling the same way about us. OP, just as you find it difficult to hear about the pain of someone who already has a child, which you want, there are those who may find it difficult to hear your venting when you have only been ttc for a relatively short time. In reality, everyone needs to be able to express their pain.
It never bothered me to be around people dealing with secondary infertility. I really believe in using our pain to connect rather than to shut people out. The only time I was really bothered by someone else's complaining was with a woman who already had 7 or 8 children who told a group of us that it was just the same as the pain of any of us who were struggling for child #1 or #2. I was not bothered that she was experiencing pain about not having that 8th child...but I did not feel that she grasped many of the issues that those of us with many fewer children were facing.
For me, the journey to the second child has been far easier than the journey to the first, but that's just for me. I can't generalize that for anyone else, and the journeys can only be assessed in retrospect anyway. For me, the difference between #1 and #2 is that when we were searching for #1, I was not only dealing with the loss of that specific child that I dreamed of and hoped for, but I was also dealing with the loss of the experience and role of being a mother. I believe they are two separate things, and that is one thing that someone going through secondary infertility is not dealing with. Now matter how much I longed for my second child, at least I was a mother, and that carried me through.
However, another reason #2 has been easier for me is because I did so much of the inner work of grieving and healing before #1 came along. And, a person who is dealing with secondary infertility who had no trouble getting pregnant the first time is experirencing all those emotions very acutely and going through the phases of grief for the very first time. It's all new territory, and I think that in itself makes the pain very intense. Also, I can see where someone who had experienced infertility prior to their first and was now dealing with it again prior to their second might have a harder time simply because of the weariness of being on the path again. They would be starting with less naivete that second time around.
It's just all so individual. When you add pregnancy losses to the journey, it brings in another new dimension of pain, which, OP, I would imagine is part of why this is so fresh and raw for you right now.
I heard somewhere that the hardest trial is the one that you are currently going through, and I think there's a lot of truth to that. We really can't compare experiences, but we do need to be able to share even our less-proud feelings.