well yeah - no material possession is worth fighting for. Except maybe Time Warrior.
Self defence techniques are learnt in situations like:
+ Someone is obstructing your nearest point of exit and you need to get through/around them in order to escape.
+ Someone has already launched an attack on you without making any demands (e.g. surprise attack). Like it or not, the fight has already started and you need to react.
Unfortunately we have certain members of our society who start fights unprovoked just because they can (typically angry people with low self-esteem who feel like randomly lashing out at strangers).