For myself I voted somewhat necessary. Although I must point out that whilst according to Dave Organ, Candian Law says you can only use the minimum force necessary in the UK (England & Wales particularly)the rules are you can use 'reasonable force' (a question of fact in each individual case) and are not required to 'judge matters to a nicety'.
At the end of the day I personally feel that my entitlement to prevent someone hurting or injuring me is far more important than their 'right' to avoid being hurt by someone they attack. I do believe that it's better to be judged by 12 than carried by six.
As far as the argument that placing a value on your own life can make cowards of us all I would say, it's sensible to value your life. But that doesn't mean that you wouldn't risk your life for something you percieve to be of greater value. In particular home and family.
Besides failuring to do anything effective to defend yourself from an attacker, means that not only will you be a victim but others are more likley to as well.
Just my thoughts