There are a surprising number of officials who might have reasonable grounds and lawful basis for entering your property, possibly without your knowledge or consent. Emergency services responding to something like a fire or a call saying someone was hurt would be an obvious example. A more subtle example might be something in your home generating noise or radio interference that is affecting everyone else in the area and needs to be turned off.
So, maybe a blanket law saying you can cause essentially unlimited harm or death to anyone entering your property without your consent isn't such a good idea? There are at least two main legal foundations in England for what we casually refer to as a right to self defence, but both of them rely on a test of reasonableness if force is used. Also, it's already acknowledged that someone's idea of what seems reasonable won't be perfect if, say, they are half-awake at 3am and find an intruder standing in the dark outside their child's bedroom, and so there is already an element of benefit of the doubt being given in such situations. Going beyond that would have to be based on either an argument that the current law isn't clear enough to make someone confident to act reasonably (which is a legitimate concern) or an argument that we want to legitimise the deliberate use of grossly excessive force (which, IMHO, is not).
So, maybe a blanket law saying you can cause essentially unlimited harm or death to anyone entering your property without your consent isn't such a good idea? There are at least two main legal foundations in England for what we casually refer to as a right to self defence, but both of them rely on a test of reasonableness if force is used. Also, it's already acknowledged that someone's idea of what seems reasonable won't be perfect if, say, they are half-awake at 3am and find an intruder standing in the dark outside their child's bedroom, and so there is already an element of benefit of the doubt being given in such situations. Going beyond that would have to be based on either an argument that the current law isn't clear enough to make someone confident to act reasonably (which is a legitimate concern) or an argument that we want to legitimise the deliberate use of grossly excessive force (which, IMHO, is not).