In the spirit of being encouraged to speak my mind here's a slight effort post:
Defederation does not do what you think it does.
The instance creator and admins are those with the ultimate power within their instance. The active users delegate them that power by interacting with their instance.
Defining "defederation" within the context of Lemmy as I understand it:
"the act of denying the ability for accounts within specific instances to interact with each other"
Anyone at this current time can create an account on most instances. One site on sh.itjust.works is defederated right now, but anyone here may also have an account there, who knows? The value comes from our activity and interaction within each instance.
Defederation is a narrow and a slippery slope because it doesn't actually solve any problems. There are many instances which are doing things I think should be banned. I don't interact with them. I don't provide them with any value.
We uphold an inclusive enjoyable community here by being active. Individuals with malicious intent are ostracized naturally by an active community. Defederating entire instances does not stop bad actors, but an active strongwilled community does.
It's not our responsibility to moderate other instances.
Thank you, I see your point now. You are worried bad actors could simply join this instance.
They could, but then they would fall under the guidelines and moderation of this instance. I'm not sure in practice how big of a worry this is.
And bad actors can join without needing to come from a banned instance.
This doesn't change my view of defederation. (I won't claim to know the correct use/threshold for defederation, this is all new to me! I'm mostly here to enjoy the discussions, not worry about what might go wrong.)