Suppose that a reporter working for a reputable news source in the United States was interested in helping his or her audience better understand atheists and was particularly interested in figuring out why some of us seem so angry. I think there are almost as many ways one might respond as there are atheists. I have provided a brief version of how I might respond below.
To understand what it is like to be an atheist living in one of the oppressively Christian regions of the United States, I'd invite one to imagine being a physician who is attempting to provide medical treatment in a primitive village that has had little contact with the modern world. The villagers are unfamiliar with science and medicine, rejecting them in favor of ineffective superstition. They believe that illness is caused by evil spirits and refuse to permit you to treat their children because their religious traditions tell them that their rituals will protect them. Although their children experience great suffering and death due to treatable illness, they remain hostile to you because they are convinced that their faith is enough. Your meddling will upset their gods, and so you are seen as a threat to their eternal happiness.
In too many ways, the modern atheist is likely to have a similar experience as this physician. We are surrounded by a form of superstition that is both obsolete in today's world and harmful to our continued existence. The "angry atheist" depiction can be little more than an inflammatory stereotype crafted to discredit us; however, it may also reflect something similar to the justified anger the physician described above would undoubtedly experience. That is, it is entirely possible that we are angry for many good reasons.
Polls have long indicated that we are one of the most hated groups in the United States, contributing to a long history of marginalization and legal discrimination. Those who despise us because we reject their preferred religion reveal that their true agenda is anything but religious freedom. When prominent political figures, including U.S. presidents and members of Congress question whether atheists can be American citizens, we are reminded of similar statements of intolerance made during the Civil Rights or Suffrage movements.
Many of us are rightly appalled at the consequences of religious faith. Each of the mainstream religions claims to have a monopoly on truth and explicitly rejects other religions as false, fueling intolerance, tribalism, and conflict. Those who equate religious disagreements with those over baseball, music, or other trivial matters reveal their ignorance of history. Religious conflict has repeatedly led to violence, and many of the worst atrocities have been committed in the name of religion. Even religious faith one might label "moderate" calls on the believer to suspend rational judgment in favor of superstition, making it difficult for believers to challenge dangerous forms of religious extremism.