If you'd likely read much at all of the extensive discussion with Nevill, you'd see why the past matters.
Well, we never actually reached a consensus.
I just acknowledged that your interpretation is internally consistent and makes sense if you want to look at it that way. It probably plays a part in their reasoning, but we still disagree on how much influence we ascribe to it.
That they view Mordred as utterly irredeemable is worrying, given that Bailey should be able to see we are sincere (if I interpret Gally's description of Bercilla's powers of Inquistor-ship correctly) when we say that we don't want to do any of that again.
But they don't?
You know whom they consider irredeemable? The Forces of Darkness. If it were, say, Sa'Lanyah in our place, her head would have rolled by now. I don't think they would have taken her prisoner to begin with. We know Bailey didn't want to take our surrender.
They see us as a wild card, with a history of mass murder and siding with their enemies. A liability to some. An opportunity to others. They are seven different people, with different experiences and opinions, forced to work together and find some way to reconcile those opinions with each other. Hence, the vote.
This isn't even a trial, I don't think. There is no crime that is judged here. There is no presumption of innocence either, which I imagine pisses a lot of people off. There is just a simple question, can they afford to leave you alive with the stakes being what they are.
It's only Bailey who sees us as irredeemable, and our entire existence a net negative for the world. We know it stems from a very... uncompromising sense of justice. It's not a rare mindset to have. If a mass murderer says he quit - does it mean he should be forgiven? Even I believe there is a threshold after which redemption is impossible.
My personal theory on her is that Bailey/Bercila has certain issues with loyalty/treachery, and holds very harsh views on those. "Once a traitor, always a traitor"; "a enemy can be forgiven, but a traitor never"; things like that. And Mordred is undoubtedly one in her eyes. He is marked and branded forever by his actions, and his words fall of deaf ears.
I can't help but think that how the team handles Lucy will have an impact on the Inquisitor. Mordred is a stranger to Bailey, easy to dismiss, but a former friend? It might make a crack in her armor of self-righteousness.
Ginny... she wants us to repent. I see people who heard she wanted us to beg, and reared up, but to me that is oversimplifying things. Annabelle's exact words were 'to hear you say that you were wrong, that you're sorry, that you're throwing yourself at our mercy'. It isn't a matter of superiority, but of genuinity. She doesn't understand how one can be redeemed when they are completely unrepentant in the face of all the horrible things they've done. If there is no guilt, then what is there to stop it from happening again when the mood strikes us?
The rest of them aren't even bent on killing us. Piper and Matthew want to use us (though Piper wants to kill us once our usefulness runs out - she is very pragmatic and leaving a wild card alive is not worth the risk with seven billions on the line), and Gavin... he is a complicated case. He is the only one who still calls us a friend, though he supports us as much for his own sake as he does for ours.
There's a sizeable emotional difference between "You're trying to kill me and I'm trying to kill you back and now you're dead" and "we're going to sit down and discuss this and then kill this person".
Sizeable, yeah. It comes from some of them leaning towards 'let me kill him right now!', and others going 'no, wait!', and then having to reach some kind of compromise that wouldn't tear the group apart even harder.
Their group is not a person, nor is it a hivemind. What looks like a premediated murder in cold blood after some deliberation is a result of conflicting personalities and agendas... which is currently working in our favor, I have to add. Were it not for this mechanism that restricts individual emotional impulses, we'd be dead right at the club.
For one, Gavin
is bothered by what you called them out for:
"What do you want me to say?" Gavin shouts, slamming his hand down onto the table. "You want me to just smile while you chop off our friend's head?"
"He was never your friend!" Bailey shouts back, pointing at you. "He's a liar, he's a killer-"
"He's in good company then!" Gavin runs both his hands through hair, individual strands of pink poking every which way. "I mean – I mean, he did some bad shit, yeah? Yeah! But what, we just kill him? We just kill anyone who ever does something shitty?
...on the other hand, Bailey is bothered by the fact they have to hold a trial at all to kill us.