What is strict liability in US law? Is it really possible for a person to be held liable who did not intend to do harm or violate a law, and who was not negligent?

(This question is in response to issues raised in answers to the question ["Is there a legal principle regarding laws that cannot reasonably be complied with?"](https://law.stackexchange.com/questions/38530/is-there-a-legal-principle-regarding-laws-that-cannot-reasonably-be-complied-wit/38555?noredirect=1#comment70143_38555)