The FBI's political surveillance was not a result of popular hysteria, such as scholars used to claim, or a rational response to communist spying and the Cold War confrontation, such as a number of historians have recently argued. Instead, it was an integrated part of the attempt by the modern federal state, rooted in the Progressive Era, to regulate and control any organized opposition to the political, economic and social order, such as organized labor, radical movements and African-American protest.
Red Scare: FBI and the Origins of Anticommunism in the United States, by Regin Schmidt, PhD
The FBI working against progress shouldn't really be surprising when this is what they did in their formative years. It's a big mistake to think we were stupid in the past and that we're above doing what we used to do, today, and I'm really starting to wonder if intelligence agencies actually are a net positive the more I read about them, at least they seem like they're well overdue for some radical reforming to ensure they act in the best interest of common people, rather than whatever they're doing now and historically.
They had info on 9/11 but didnt put the pieces together.
The BLM protests... Are protests? Do you want the feds to stop protests? Don't worry, feds were on the scene doing all kinds of random shit like entrapment and interrogation and whatnot.
They did see Jan 6th coming, but basically chose not to interfere.
Why keep them? Theoretically surveillance can be useful. Its hard to justify understaffing and downsizing. I'd choose complicit. A lot of feds are fascist. They're smart, unlike cops, but they're evil just because of pathology or whatever. TBH the kind of person the FBI recruits would likely be even more dangerous if they weren't agents.
Thinking of this from the prospective of "why have an IT department we don't need them everything is working". At least hopefully they have mitigated / prevented similar events you listed and we just never heard about them.
Federal investigators foiled a massive bomb plot brought on by ~20 domestic terrorists who immigrated from another, restless, country and thought that wanton destruction would somehow galvanize support FOR their position on the conflict back home.
Can confirm that OUR feds are worth their (really small) pay.