What if youre asleep? A house with no lights on and someone asleep upstairs looks a lot like a house with no lights on and someone on holiday, especially to the casual criminal. The law must take the standpoint that one can only take a life if you or someone else is directly threatened by another. Simply breaking into your house is not enough justification for the killing of another - there must be other factors present.
It already takes those factors into account. It recognizes that a home is not the same as an office or store, where one can expect it won't be occupied after business hours. The very purpose of a home is to be inhabited at night. The law presumes in favor of the homeowner, and rightly so. What standard would you accept? Allow the homeowner to fight back after the home invader demonstrates his intent with a couple of shots or stabs?
As for the Martin situation, honestly, I don't have an opinion on it. He did something stupid, but the "victim" was scum.
One clarification is in order, to forestall the typical argument about the law not giving homeowners the right to execute someone. What the law recognizes is that in the confines of a home where you generally don't have the means or duty to retreat safely, if you kill an intruder, the belief that the person's uninvited and unrestrained presence is a threat will be deemed reasonable. If you order that person not to move and/or to leave, and they comply, then you do not have the right to pop them in the back of the head as a summary sanction for waking you up. If they refuse to comply or engage in furtive movements after seeming to comply, the presumption that they are up to no good remains.