Zed,
"We have this one poster who argues I should be terrified of Islam as a threat to Western Civilization."
Right now, atheists and Muslims may not see themselves as being in direct conflict. In Western politics, they may find themselves on the same side in opposition to traditional Christian and Jewish influence.
Just wait.
I think that alliance will become much harder to maintain as Islamic influence grows in Western institutions and communities.
How will atheist parents react if their children start coming home from school praising Islamic beliefs or bringing Islamic religious practices into their homes?
Think that can't happen?
At present, Islam is often far more assertive than modern Christianity about maintaining visible religious practices and seeking accommodations for them in public life.
Some of the people who currently regard Christianity as the greater religious threat, may eventually find themselves confronting a religious culture whose expectations are considerably less compatible and more objectionable to their own secular beliefs. Muslim values are stricter than what they are accustomed to.
Also, Christianity in America generally does not require public rituals performed several times a day that can affect everyone around them. Islam has practices that many Muslims regard as religious obligations, and American religious freedom laws can require governments and institutions to make reasonable accommodations for those practices.
Right now, secular people may be saying, "Why should I worry?"
Some of the same secular people who strongly defend Islamic religious accommodations today may eventually conclude that what they regarded as harmless accommodations was a Trojan horse.
