Personally, I shoot strays immediately if they don’t have collars. If they have collars they get a pass unless they are mean. We’ll contact the owners if they have tags, and run them off if they don’t.
To answer your question about definition of threat, here is what Iowa law is:
351.26. Right and duty to kill untagged dog
It shall be lawful for any person, and the duty of all peace officers within their respective jurisdictions unless such jurisdiction shall have otherwise provided for the seizure and impoundment of dogs, to kill any dog for which a rabies vaccination tag is required, when the dog is not wearing a collar with rabies vaccination tag attached.
CREDIT(S)
Amended by Acts 1961 (59 G.A.) ch. 193, § 9; Acts 1994 (75 G.A.) ch. 1173, § 33.
351.27. Right to kill tagged dog
It shall be lawful for any person to kill a dog, wearing a collar with a rabies vaccination tag attached, when the dog is caught in the act of chasing, maiming, or killing any domestic animal or fowl, or when such dog is attacking or attempting to bite a person.