Is secularism a religion? David Klinghoffer thinks so:
For each element in the Judeo-Christian family of faiths, secularism has its counterpart: a strict ethical code, albeit focusing on health issues ("Thou shalt not smoke," etc.); the use of shame when individuals disregard ethical rules (e.g. fat people); a related promise of eternal life through medical advances; a creation story (Darwinian evolution); and so forth. All that's missing is a deity, but not every religion has one, as the case of Zen Buddhism attests.
All this would be fine-after all, America is a big country with plenty of room for every spiritual predilection-but for the tendency of secularists to use aggressive means in advancing their political agenda and spreading their faith.
Consider state education, where the secular church has ensured that its creation account alone be taught. According to the Discovery Institute, Ohio, Minnesota, and New Mexico are exceptions to this rule, now requiring students to know about scientific evidence critical of Darwinian evolution. Everywhere else, evangelism for this secular doctrine is a staple of 10th-grade biology class.
The prejudice on behalf of the secular faith emanating from the media is likewise hard to ignore. HBO's Bill Maher, raised Catholic but later converted to a harsh secularism, is among the frankest of news and entertainment industry figures in his contempt for competing religions, notably Christianity. The host of Real Time with Bill Maher speaks of himself as "spreading the anti-gospel."
There's more at the link. Klinghoffer might also have mentioned that secularism has a de facto clergy comprised of university scientists, a dogmatic adherence to faith in naturalism and Reason, and a creed (e.g. The Secular Humanist Statement of Principles).