when is it "ok"?

[Jack]

Andy has a good point- defend life, not your TV set.
Regulations vary from state to state, and it's important to know what the criteria is in your state.
I think in your house has a lower standard of 'ok to shoot' in most states than outside the home. Outside the home, for example on the street, in a parking lot, a question a DA is going to raise right away is "could you have run, rather than shot?".