I realize that any discussion that touches on secularism can't satisfy the subject without addressing religion as well (secularism being, by basic definition, the separation of church and state), and that all discussions with regards to religion end up polarizing the interlocutors. But as the saying goes, sometimes a man gotta do what a man gotta do.
There's a school of thought out there that argues that if a majority of people in a society thought it's in their best interest to adopt religion as a reference in legislation, then, by the virtue of democracy, their wish must be granted, and that we, indeed, ought to regard this process as purely democratic.
I can not disagree more.
It's sometimes forgotten that democracy, as outlined by its pillars, is far more encompassing than the simple concept of majority rule. Freedom (of choice, expression, etc) is a quintessential part of democracy. Respect of and accommodation of minorities (a sect, religion, school of thought, or a political view that form a minority group in a society), is another quintessential part. Equality of individuals before the law, regardless of their religious leanings, is also an indispensable part of a democracy.
The question that presents itself here is: is there any theocratic set of laws on the face of the earth that satisfy the above parameters?
I'll volunteer and say: no, there isn't.
Any law that is derived from a scripture is, by default, designed to serve those who wholeheartedly believe in that particular scripture and its religion. The 'others' are more or less considered inferior, or in at best regarded as different, and hence bestowed upon with a different set of rules. This arrangement negates equality and treats individuals on the basis of their religious views (or the lack there of). As far as I'm concerned, marginalizing those who do not subscribe to your world view and calling yourself a democracy is a very unfunny joke. It's no wonder, or a coincidence, that 'minorities rights' is a determining factor in the democracy index. Of course, majority will have to decide (either directly or through representatives) when it comes to the things that require collective agreement. But that doesn't mean that a majority could render a minority inferior or non-equal since they do not conform to the view of the majority. Suggesting that that could happen in a democracy is suggesting that a democracy is innately suicidal and self-negating.
Secularism is the indispensable, inseparable companion of democracy. When you impose the laws of the scripture on people, it will be considered an affront to God when an individual breaks that law, not merely a violation of a law (as it should be deemed). Please be advised that I'm not anti-religion, nor I'm against religious parties participating in a political process (under the condition that they observe the secular components at all time). The question, then, whether I believe in God or not is irrelevant.
Eventually, if a majority decided that their society must adopt a scripture as a legal reference, then it's all good and dandy. By all means go ahead and do it. But please, don't call yourself a democracy, 'Pluralistic Theocracy' or 'Mulla rules by rotation' could be more accurate.
Religion is a wonderful thing. Its beauty is characterized by it being personal and spiritual and private. Religion is best practiced at Churches and Mosques. Let's keep it that way.