1) Property destruction has always been a weapon of resistance for those who don't own property. Property is theft, by a few of the many.

2) Grafitti, detournement, reclaiming space, etc. are methods WITHIN A STRUGGLE, whereby we reject both legalist or moral arguements. ie These ideas of right and wrong are fluid, and are often subject to change. Case in point that grafitti is an important social movement in the US, and everywhere militarized space exists. However, classics both deny that ..our own history.. while generating absolute morals
quote "respect for other people's property is important" end quote
which implicitly negate a legitimate usurping of a space that is contested.

3) One might say that criticizing 'vandalism' is a classic liberal position: holding ideals of 'equality' and 'fairness' up as replacement for an understanding of social struggles or situations, in which one is often induced into fighting for what they already have( maintaining the status quo) rather than for a destruction of the power structure.