I fully agree on that front. However, when lethal force is in fact the force necessary to subdue an attacker, then it is legal.
The problem I see though is that the law gets messy in the case of a riot. If a group of crowbar wielding thugs are standing in front of my home and smashing it, technically my own life and body might not be in danger. As for defending my property, I could go behind a man and grab him in a bear hug and make a citizen's arrest. Fair enough.
Now if all the others start yelling a me to release him, this is where the law gets messy. They're still not technically threatening me, yet I must assume that if I keep holding him they could hurt me. But if I release him, then I forfeit my right to make a citizen's arrest. At that stage, I'd say the law ought to grant me the legal right to release him and immediately turn on the others who were yelling at me, and use lethal force, the argument being that owing to their superior numbers, I have no choice but to use lethal force to compensate. And even if they have not explicitly threatened me, the fact that they are defending a person who has used violence against my property should stand as evidence that they do defend violence, and so are likely violent. Since they outnumber me, and I have only two arms, there is no way I could arrest them all. As a result, preemptive lethal force is my only safe option to defend my right to make a legal citizen's arrest to defend my property. Certainly I ought to target my attack exclusively to those who have shown verbal aggression towards me by telling me in a threatening tone of voice to release someone I was not harming but merely arresting. And of course the second they disperse or run away, I should immediately cease form using lethal force, but still reserve the right to chase after the one who smashed my window to make a peaceful citizen's arrest, and again be free to use lethal force against any organized group interfering with this right.
Not lethal force, but the right to maim, such as by aiming for the legs or arms for example.
Of course they should be taught to use the minimal force necessary to defend themselves and their property. Though sometimes lethal force is the minimum force necessary when you're outgunned and outnumbered.
To the best of my knowledge, the law is similar in both countries. You are expected to use minimal force. And in both countries, lethal force is acceptable if that is the minimum force required.
The problem of course comes with interpreting 'minimum force', and when we would consider lethal force to be the legitimate minimum force required.
Essentially, I'm proposing that when we face an organized group of outlaws, that we define minimum force a little more loosely to take certain factors such as numbers into account.