I am a feminist because I understand that our society has been prejudiced in favor of the masculine for more than 2000 years. That prejudice has deeply affected our thinking; we are conditioned to accept certain modes of relating to each other based on a power structure that defines our "god" as a "he". Whether we like it or not, the "ultimate" authority for the majority of people on the planet is not "goddess."
Feminism, as I see it, is an attempt to bring the situation to the light. It is an attempt to make conscious the conditioning we have been exposed to, the modes of thinking that affect us. It is a statement that says "let's examine this" and "let's move forward." It is about furthering our evolution – the evolution of our consciousness.
Now, that being said, I will also note that I do not agree with every "feminist" who has ever given a speech or published a paper. Germaine Greer, for instance, makes me livid with her attitude toward trans women. I also want to recognize the failure of the movement to capture the attention of young women, like, for instance, my daughter, who when asked if she was a feminist replied that she was not. I did not argue with her; but I was saddened. I am pretty sure that she equates feminism with lesbianism to some degree, and with being angry as "Lightbulbs"(above post) has alluded to. My daughter also resists the idea that we replace male power with female power. I consider her resistance to be a philosophically wise position, and am saddened because feminism gets the reputation that it wants to replace patriarchy rather than transcend it.
But, for myself, I don't throw feminism out the window just because it is not perfect. It takes courage to own up to an idea fully and see its evolution. I affirm that courage in me. I am a feminist.