I think there's a difference between showing kindness, compassion and acceptance, and accepting everything.
You can show compassion and acceptance for alters and their feelings, yet set boundaries for the way they express/act those feelings.
Our own persecutor was really hard to deal with, and finding balance between compassion and what was okay to accept wasn't easy. Working with him taught me how to make the difference between the individual and their behaviors ; unlike what our abuser taught us, you can feel compassion, and even love, for the individual, yet it doesn't mean you have to accept all of their behaviors. Love, compassion and understanding doesn't mean accepting everything. You have the right to say "stop" or "no" when someone cross your boundaries, and it doesn't mean you don't empathize with them. It just means you have your own limits, and yes, they should respect them.
For each unacceptable behavior Claude had, I had to dig and find the core reason why he was acting like that (which he often didn't really know himself), then reassure him and talk about other ways to express those feelings. At the beginning, I had to talk kind of the same way as him to be heard, like :
"Okay, I get it, you're scared, so I will not do this/not do this again. But you know, that's not really smart to trigger a panic attack or a flashback into another alter. You could have talked to me instead."
And he would just laugh, or told me I was stupid
But slowly, he saw that I meant it, and that everyone inside agreed with me. If anyone inside is scared or angry, they can talk and it will not be used against them. And I think it's something important in the healing process of persecutors : if there's one alter who's not ready to make efforts and to follow the others in order to have a common way to deal with them, it will not work, or be harder than it should.
But I totally get that having everyone acting the same way isn't easy. It took some time to us too, but all of our system slowly stopped being angry or resentful toward Claude and began to act the same. When he was harassing another one (usually Kal), instead of yelling at him or running away to hide, this other alter would come to me, so I could deal with him (each time with "You feel this and I understand why, it's okay to feel that way and I can try to do this to help you, but it's not okay to act like that, you could have done this instead").
Once or twice, he triggered another one just to see our reaction. The last time he did that, I lost it and went angry, telling him he was stupid to act this way because the system was the only thing he had left, we were the last ones caring about him. At the moment, he told me he didn't care, but now he admits it was the first time he realized that I really, really meant it and it scared him to think I was telling the truth ; that he wasn't alone against the world like he thought, and that I would never tolerate his destructive behaviors, not even against himself, because I cared about him. It was the first time he felt that someone could really care about him.
He never tried to trigger anyone again after that.
As Claude saw that the boundaries were coherent and consistent, he finally become tired to be seen as the unstable one every time he acted, so he started try to calm down and to follow my suggestions.
When he saw that no one was making fun of him for doing so, when he saw it worked better than his previous ways, when he saw my suggestion and rules weren't unsafe like he expected, when he saw he still could be himself and deal with toxic people (our family) the way he wants if he waits for our approval (right now, he almost stopped to ask, he totally trusts Daem to deals with them), and after a specific event which proved to him we were ready to protect him just like we would protect anyone else inside, the system became a synonym of safety and support for him, and he started to want to change and to make efforts too.
I don't need to use negative critics like "it's not smart to..." anymore with him as it would be totally destructive now he sees me as a mother figure. I just have to tell him to stop, and most of the time, he will listen. Sometimes, he tries to argue, but it's less and less common.
He still doesn't really believe he has our support, and he's so scared of loosing it, he freaks out every time he is triggered and breaks the rules I've set, even when he is right to do so.
But after becoming aware of his presence and finally finding the courage to deal with him (which took us years), it took us again two years of hard work to reach that point. We even had times when we thought we would never make any progress with him, but he totally surprised us - in a good, very good way.
All of this to say I agree, you don't have to accept the unacceptable, but that doesn't mean you can't show empathy or kindness. And yep, it's not that easy to learn to do both as, usually, no one taught us ; most of the time, our abuser taught us that if we weren't ready to accept everything, it meant we didn't love them or weren't able to understand them. No one taught us the in-between and how to deal with it.
As a side note, I think that's why persecutors can be so hard to deal with. Just like our abusers, they tend to think that if you put boundaries, it means you don't love/accept/understand them, so they react. When the rest of the system think this way too, you end up totally stuck.
I was stuck for a long time with Claude because of this, and since we've started to work with him, I can't count the number of time I had to told him "I say 'no' because of this and that, not because I don't love you, okay ? I really love you, but if we do this, then it will lead to this and that. Got it ?". Sometimes, he's so easily triggered that I need to say this for something as insignificant as saying "no" for one more coffee. And he hates when I do that, because he hates being reassured like a child... but he also admits it's the only way to not have him react because of the fear of being rejected. And maybe, deep down, he finds it a tiny little bit comforting too

We hope things will get better for all of you.
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French person with ADHD
Former partial DID
Functional multiplicty, highly integrated