I think a good compromise would be to place them on a list to be manually reviewed by humans. I've seen those brigades so I think you make a great point.
The mentality of "I haven't seen it so it must be that it doesn't exist" on some of the replies here is weird.

I did see something similar with two posts of the gnome tiling feature in the same community. The first one had mostly positive comments, while the second one had mostly negative comments. (It seems it did get a few positive comments since I first saw it, but overall it's still more negative)
The articles the posts link to are different, so that could influence things. Still though, it's the exact same feature being talked about so it's weird to see such a strong difference in the majority opinion under the posts.

In case that helps in any way, ctrl+shift+t is the shortcut for undo close tab. It's one of the most helpful browser shortcuts I know.

I really don't think the firefish admin "has no issues with racism". The "evidence" there is that Kainoa (the admin) boosted a link to an Electric Frontier Foundation page sent by Eris. I think that's a ridiculous conclusion to make.

I think it's too hasty of a conclusion to say they were doctored, at least based on what I saw following the situation. There were suspicions/allegations of it, but no clear evidence.

I like Calckey the most as it has the best thread view out of all fediverse software.
Akkoma is simpler and more lightweight if you prefer that, but I find its thread UI hard to grasp.

I don't think it's comparable since fediverse is human moderated and email is not. Messages and accounts on the fediverse are public, so moderators can remove spam before other people see it.
Accounts on existing instances can be removed and dedicated spam instances can be blocked. The only thing it does is increase the toll on moderators.

I think a big problem specifically with mastodon.social is its sheer size. I think it's harder to effectively moderate it because of it. If the spam attack was directed at a smaller instance it would also be easy for other instances to hide or block it until it'd be sorted out, so the surface area the spam would reach would be smaller.

The license in the repo is AGPL. Misskey which Calckey is a fork of has the same license.