I first became an anarchist when I was about 14 (about 2 years ago). The basic philosophical reasons that I am an anarchist can be summed up as follows:
1) It seems obvious to me that freedom and democracy are values to be treasured, and that the closer a society comes to complete freedom and democracy the more ideal that society will be. Consequently, the closer an individual comes to general freedom the more opportunities they have for happiness, self-realisation, and prosperity, and the closer a society comes to genuine democracy (i.e. all of the institutions of society are collectively run by all in them on the basis of equality) the more just, equal and desirable that society will become.
2) It also seems obvious that hierarchy, domination, and concentrations of power have inherently negative effects on society, and the closer a society can get towards the abolition of hierarchy and of the divisions between ruler and ruled the more ideal that society will be, and the more it will be able to move towards freedom, democracy and other social structures that seem obviously positive to me.
3) It also seems obvious that when power is concentrated in the hands of a few, the few that has power is forced to commit great crimes against the many, subject the many to constant exploitation, and bring many other undesirable traits to society, in order to maintain their position of disparity. This point works out almost perfectly in practise, as the history of states, capitalism, state socialism, etc. demonstrate.
For these reasons (which are completely simplified here, but still hold true I think) I think that the closer a society moves towards the anarchist ideal the better it will become. The question from there is; is anarchism possible? I think that the history of anarchist experiments has shown that it is. But even if it isn’t, if we struggle to obtain the anarchist ideal we will gain as much freedom and democracy as is possible and as little hierarchy and domination as is possible, which seems obviously a good thing.