I was asked this question in a recent comment, and I do believe some discussion is warranted. Maybe I will even be able to use this post to answer the question the next time it is asked.
To begin, let's agree that "hate" and "disagree with" are not the same thing. I can disagree with you but still respect, like, or even love you. Disagreement with someone's beliefs and/or opposition to one's agenda should not automatically imply hatred of anything or anyone.
With that behind us, I do disagree with Christianity and all other forms of religious belief. Why? I'll pick one of many reasons for this short post. All the major religions claim that supernatural entities exist. However, we have no evidence whatsoever that these things exist. Not one shred. Thus, reason, intellect, science, and even common sense lead me to conclude that there are likely no gods, demons, angels, ghosts, or supernatural entities of any kind. If the existence of any of these beings is conclusively established in the future, I will gladly admit I am wrong. Until then, I will continue to base my worldview on the available evidence.
At this point, most theists will feel compelled to say something about faith. After all, faith is required to believe in absurd notions for which there is no supportive evidence. But I reject this sort of faith as a destructive departure from reason that has dire consequences for humanity (see Sam Harris' The End of Faith). To suspend reason by embracing superstition is to delude oneself into a blissful but counterfeit state of idiocy, one which history has taught us repeatedly leads to bloodshed.
Now, let's return to the original question. I've provided one reason why I disagree with Christianity, but why aren't I content simply to maintain my worldview and not cause any waves? In other words, why have this blog at all? From attempting to restrict a woman's reproductive freedom to international terrorism, I am deeply upset at what I see people doing in the name of religion, including Christianity. My fellow atheist bloggers and I seek to provide a voice of reason. This voice may take the form of polite criticism to loud opposition fueled by disappointment and anger. However, the motivation to speak out is the same - we are horrified by the effects of religion in the world and encourage its abandonment.
I do not hate Christianity; I disagree with it, and I believe that it and other religions are detrimental to humanity.