The notion of an Englishman's home being his castle, and defedning hearth and home and all this is all very laudible but ...
before very long, you have to start justifying all manner of acts of violence - you are into the "I thought he was going to stab me so i stabbed him first ..." situations, and onwards and downwards from there.
For this reason - not individual cases which are apparently as black and white as this one - but the hundreds of 'not sure of the facts' tragedies that can follow, we must never simply accept that an offender 'got what he deserved'.
It is too simplistic, and it leads to a cheapening of human life which has seriously far reaching consequences - so let's not be too quick to pay this guy on the back and buy him a pint. After all, i doubt he feels like celebrating, having taken a life, no matter what the circumstances.