It’s a term I see more and more, and I’m worried that it’s degenerating into either a redundancy, or code language for “atheist left.”
Ann Althouse linked this WSJ Op Ed by First Things editor Joseph Bottum which has the following subtitle:

Will the secular left soon attack the religious right for being pro-science?

In her analysis ,Ann Althouse puts the conflationist term “secular left” in quotes. I think she’s right, because the term merits attention.
While I can’t read the mind of Joseph Bottum, I don’t think it has quite the same rhetorical ring as the accompanying overused term “religious right.”
Or does it? When I think of the “religious right” I normally think of moral or social conservatives, usually fundamentalists, who tend to be in the conservative wing of the Republican Party. As opposed to the non-religious or less religious right. Goldwater conservatives, paleoconservatives, libertarian Republicans, and even some neoconservatives are by no means necessarily fundamentalists, and thus they do not all deserve to be lumped in with the “religious right.”
But is “secular left” used the same way? Is it used to distinguish the secular from the non-secular left? Or is it code language implying that secularism is inherently leftist?
I don’t like the automatic assertion that there is no such thing as the secular right.
This tends to be a kneejerk assumption among conservatives, but more than one conservative has objected.
In a great article titled “The Secular Right,” Robert Tracinski explains:

If a young person is turned off by religion or attracted by the achievements of science, and he wants to embrace a secular outlook, he is told–by both sides of the debate–that his place is with the collectivists and social subjectivists of the left. On the other hand, if he admires the free market and wants America to have a bold, independent national defense, then he is told–again, by both sides–that his natural home is with the religious right.
But what if all of this is terribly wrong? What if it’s possible to hold some of the key convictions associated with the right, being pro-free-market and supporting the war, and even to do so more strongly and consistently than most on the right–but still to be secular? What if it’s possible to reject the socialism subjectivism of the left and believe in the importance of morality, but without believing in God?

Tracinski links an article by Heather Mac Donald that created quite a debate, and which was addressed by Michael Novak at First Things.
Interestingly, there’s a Wiki entry on the subject of the secular right, but this is defined as “refer[ing] to but [is] not exclusive to the libertarian, socially liberal or non-religious wing of most conservative movements or parties.”
At the time of the founding, there were plenty of religious secularists, who wanted to separate government and religion not to the detriment of religion but for the benefit of religion. In a post on the subject, I quoted James Madison:

The settled opinion here is, that religion is essentially distinct from civil Government, and exempt from its cognizance; that a connection between them is injurious to both…

Of course, the word has been so misused that for many conservatives it’s come to mean official state atheism which is just awaiting the opportunity to bulldoze churches.
“Secular” has become such a dirty word that few on the secular right would dare define themselves that way.
And the endless conflation goes unchallenged….