Knowingly or negligently materially supporting violent crime creates criminal liability under conspiracy statutes. Plenty of states specifically regulate domestic terrorism [1]. And as we've seen with gun violence, by default being involved in acts of violence generates civil liability [2].
Negligence is generally not sufficient for conspiracy statutes, and Flock wouldn't have to be knowing or even negligent. Indeed, there is no possible way they could prevent their services from being used by violent insurgencies except to not sell them at all.
> Flock wouldn't have to be knowing or even negligent
Neither do banks.
> there is no possible way they could prevent their services from being used by violent insurgencies except to not sell them at all
Prevent? No. Increase the cost of? Yes.
Trying to police domestic terrorism by restricting what they see is a bit silly. But if that were a concern, I said "make the database operators strictly liable for breaches and mis-use." Domestic terrorism is mis-use. But it's not precedented mis-use, which makes it a strange priority to get distracted by.
Existing liability law works just fine for terrorism. (Guns notwithstanding.)