Thx1138 self defense is less a legal minefield and more a factual one
The problem with this though, is that it can often be quite difficult to establish what the facts are. If you take the scenario the OP describes, we have very little information as to what actually happened. What was the situation/history that led to the incident, what was said exactly, physical characteristics of both parties, previous convictions etc. If you imagine that scenario with no witnesses, no cctv etc, then what you have is someone who’s been headbutted, and someone admitting to doing so. Very possible the police would see the actual admitted ‘assault’ as the greater crime than the alleged ‘threat’.
So each incident would have to be carefully examined on it’s own merits, and all factors taken into account, and then it’s often down to the interpretation of the courts. Seldom very simple.
I don’t think it’s fair that you can be judged as to what is deemed acceptable in defending your own home, when you decide you need to fight you have to turn off a switch in your head and in the heat of fear mixed with aggression anything can happen. Burglars should expect that.
As much as it may be exciting to fantasise about what macho things you’d do if faced with an intruder, as a result of recent knee-jerk legislation regarding reasonable force in home invasion, burglars will inevitably go armed if they fear a greater threat. Human instinct. And then begins the arms race. And eye for an eye leaves us all blind.