This is maybe not too related to the brain damage stuff (or maybe it is?), but I don't think the wider public knows nearly enough about the frankly shocking kinds and amounts of criminality in the various US special forces units. OP is not kidding about these people operating as gangs (but worse, because they're sanctioned killers).
A smattering of such behavior:
https://www.politico.com/news/2021/05/07/internal-study-defe...
https://news.usni.org/2021/01/24/seal-sentenced-to-10-years-...
https://abc7chicago.com/us-navy-seals-seal-training-drugs-in...
The journalist (and Army vet, iirc) Seth Harp does yeoman's work on this topic, and is a good Twitter follow. He's got several excellent long-form investigative articles, often for Rolling Stone. Here's one on the rampant murders (ongoing!) at Fort Bragg that the Army won't talk about:
https://www.rollingstone.com/culture/culture-features/fort-b...
And another one about rampant drug deaths at ... also Fort Bragg:
https://www.rollingstone.com/culture/culture-features/inside...
I think it's time to have a big cultural conversation about how much our current era of spec ops worship is worth all the war crimes and other less-than-normative behavior.