**Check *local* laws**

Yes, that is how it works in the USA and it is the inevitable consequence of the Bill of Rights. BUT check precedents in your state and Court Circuit: you might still be required to, for instance, call 911 after shooting, or things like that, in order to avoid a charge. In general, in no state will it ever be 100% illegal, but in some you could have more of a field day than in others.

That said

Britons, you're screwed. It's downright illegal in Britain to use lethal force in that case, so you'd be charged.

Over and over, the safest is, check local laws AND precedents on how they've been interpreted.