I highly recommend reading Don’s latest post for some important context to the following (hopefully) succinct post.
As Don argues, radical secularism can be viewed as its own sort of religion whereby the “state” replaces the religious function and, despite claims otherwise, also assumes the role of the “higher power” [God]. It can be safely assumed that most secularists are on the political left and have a tendency toward moral relativism, which is the belief that we all live by our own moral code and “whose to say one is better than the other.” However, in truth, secularists do belief in a set of moral truths: those that they determine.
Without getting too far into the weeds, even secularists realize there must be some kind of basic moral ruleset by which society must be governed. However, they have no room for religiously informed morality within government and purposefully have read the “separation of church and state” to mean the “separation of religion and state.” To them, because religion is a private matter, it is improper for a state to derive its morality from religion (especially Judeo-Christian, I might add). However, secularists, some might say arrogantly, believe that men, usually highly educated intellectual such as themselves, are perfectly able to arrive at moral truths through rational reasoning. Once “discovered,” these moral truths are best enforced by being codified into the rule of law. Thus, if its legal, it is moral.
On the face of it, it seems to hold that morality and legality are equivalent, but this is not necessarily true. For instance, most would agree that murder is both illegal and immoral. However, persuasive arguments have been made that both abortion and the death penalty are legalized murder: they may be legal, but they are immoral. So, while it is obvious that there are some gray areas, it gets even worse when reinterpreting seemingly obvious laws (or even terms, like “marriage”) is deemed appropriate and necessary to reflect society’s “proper” morality.
Ideally, lawmaking would be done through majoritarian political machinations. If most people agreed with a proposed law, it would be passed and would become the law of the land. However, to a secularist, if that is not possible, then relativistic reinterpretations of past laws are perfectly legitimate (so long as the reinterpretations mirror their “reasoned” morality). Therefore, it is important that people with a proper ideological view get placed within the ranks of those who can dictate and reinterpret law: the judiciary. Thus, a secularist’s religion is government (especially the judiciary), his dogma is the rule of law (“properly” interpreted), and his high priests are judges.