My opinion about Tartah discourse is let people be angry. I think Tartah is a wronged party, but he also wronged Coco. Hurt people can hurt other people too. Depending on their experiences, one can relate more to one side or another.
For someone who was never experienced Tartah side of the story but do have something outed forcefully similar to Coco, it hurt. I disliked Tartah for that act despite really liking him before. And it's fine. People are angry with Agott after the 1st test, angry at Qifrey after ch 40, I am angry at Oru after ch 93 - as the story progress those feelings will change - because WHA is such a story that provokes such thoughts and emotions. (1/2)
I do agree with you for the most part. It's okay for people to dislike Tartah, he violated Coco in a way that clearly hurt her and the framing of the scene made it very clear that Tartah was not in the right during the interaction. While it's clear to me that he was not intentionally being malicious, that doesn't negate the pain he caused with his actions.
People have a right to not like him after a scene like that, especially with it being his last appearance within the manga up until this point. I have never had to deal with a situation like Coco & Tartah's personally, and I cannot police how other people feel about his character. I just want people to keep an open mind about him, and remember that he isn't a villain as much as he is another victim of the same situation lashing out in a way that's hurting both himself and someone he considers a friend. He's a morally grey child, and I hope the people who don't like him now still choose to keep an open mind with him as he returns to the main story, rather than completely write him off as unforgivable based on a single bad moment.
My only issue with your opinion is in the second part of your message, and I will admit that it might be a little on the nit picky side.
"I think he did wrong in that confrontation. Why confronting Coco (formerly Outsider who knows less than him) but not Ininia who experimented on Coustas at the first place? He is punching down. Angry at one who was as powerless as he is - but he could as easily force the truth spell at Ininia and ask question. But he did not.
He could ask Coco nicely, after everything was over. He could focus more on Coustas - who just tree-d, but he didn't. He focused more on his own hurt that he did not think about Coustas, Coco, those in the Healing Spire - or even his grandpa. I am angry at him, but also curious where his story is going.
While Coco was the wrong person for him to lash out at at the time, I can see why he might choose to go after her rather than Ininia for a reason that isn't just him "punching down" at another victim.
Throughout the story, Tartah has confided a lot in Coco. When they met, she was another outsider who showed him kindness and helped him regain his love for magic, and in return he shared a lot with her despite his growing trust issues. He trusted her enough to let her know about him studying herbology with Custas, despite the fact she could easily turn him into the Knight's Moralis for studying medicine as a witch, and he trusted her with his doubts in the Pointed Cap system.
He not only views Coco as an equal, but as a friend. He's doubting the entire society his life has been built around, but he's trusting her. And unlike the reader, he doesn't know that Qifrey only told Coco about the Silverwood maybe 10 minutes ago. As far as he knows, this is a secret that Qifrey told her a long time ago and she didn't tell him about it. As far as he knows, the girl who he's told all his secrets to has known that their friend would be hurt like this from the moment they found out he was a brimmed cap, and just didn't tell him.
It's also to note that Tartah's first appearance in chapter 87 is standing with Ininia, and it's presumed that she's the one that told him about the Silverwood as by the time he first talks to Coco, he already has some level of understanding about what's happening. There's no need for him to force the truth seal onto her because she already told him what he needed to know without it.
From that perspective, I wouldn't say it's crazy for him to feel the need to be upset with Coco rather than Ininia. Unlike with Ininia, who has always been antagonistic towards him, Coco was a friend. She was someone he trusted. It's one thing to be betrayed by someone you only ever knew as a terrible person, and it's another to be betrayed by someone you trusted— especially when you already lack trust in those around you.
Yes, he could have just calmed down and asked Coco once everything was over, and I'm sure that if he did do that she would have told him without the need for the truth seal. But he's young, hurt and he feels betrayed. He's not thinking rationally, he's thinking that his best friend (almost) died and his other best friend has been keeping a major secret from him for who knows how long. He makes a rash decision, he hurts a loved one, he chooses to abandon the society that has continuously abandoned him at every turn. He's not meant to be in the right, but he's not the villain either.