BSK presented this challenge, to present a coherent argument against homosexual marriage, in his recent comments:

The fact is you haven't presented any legitimate, rational arguments against gay marriage. You have pushed your bigotry and hid behind a bunch of thinly-veiled pseudo-arguments but could not actually demonstrate how you (or any other hetero individual) is adversely impacted by the elimination of the denial of marriage to same-sex couples.

You claim to have demonstrated a rational discussion of the topic, but any rational rebuttal to your argument has simply led you to spin in another direction. So, answer the question: How are you harmed by gay marriage?

And, if you want to deny your bigotry, why do you insist on bringing up stories of negative interactions with gay men that are in no way related to the conversation? To slyly justify your bigotry? To paint the group with broad strokes? Simply saying something does not make it true. You have not been rational. And you have been bigoted. If you disagree with this, PROVE ME WRONG.And if you are going to point to biblical justifications, then I'll have to continue to call BS. First off, there are a host of things that the bible considers sinful or otherwise opposes, yet I do not see you approach such topics with the same vitriol. Secondly, seeing as how we are not a theocracy, our legal opinions must, specifically, NOT be informed by scripture. Thirdly, the bible (as are most religious texts) is full of bigotry.

And if you are going to point to biblical justifications, then I'll have to continue to call BS. First off, there are a host of things that the bible considers sinful or otherwise opposes, yet I do not see you approach such topics with the same vitriol. Secondly, seeing as how we are not a theocracy, our legal opinions must, specifically, NOT be informed by scripture. Thirdly, the bible (as are most religious texts) is full of bigotry.

The constraints are these:

1) The arguments must be rational

2) The argument must show how gay marriage affects others

3) The argument must contain no Biblical references, or be informed by Christian theology

The direction we will take is to first examine the constraints that BSK has placed on the argument.  These constraints are problematic and appeal to a method that seeks to find its end by limiting the scope of the discussion.  The secular and rational components can be dealth with first as inappropriate constraints.  After that we can present the case against homosexual marriage.

Undefined Secularism

The idea, the principle, of secularism can be defined from two perspectives. On the one hand, secularism is the non-inclusion of religious language. The U.S. Constitution, for example, is secular because it does not contain any overtly theological language. It is passive on the subject. On the other hand, secular may also be understood a the active, intentional rejection of any religious language. Again, the U.S. Constitution is, by this definition, not secular because it does not reject religious language from either the nation’s social structure or local laws. The only specific religious statement concerns religious tests for office. Even here, however, it says nothing about the character of the candidate, but only about restrictions placed upon candidates. In other words, this statement merely enforces passive neutrality on religious questions.

In this light it is easy to see why, early in our nation’s history, religious live was neutrally promoted and at the same time no denomination was promoted. It was not until the late 20th century that the definitions began to change so that even a neutral promotion of private religious behavior would become criminal (unconstitutional).

BSK leaves his call for secularism with the latter position -- that religious should necessarily be excluded (unless, of course it would agree, inwhich case I'm certain that he would accept such language).  That demand is rejected for two reasons.  First, because it is contrary to our history of democracy and open debate; second, because it places an unreasonable constraint on both the nature of the argument and those who are allowed to participate in the debate.  It is a shallow attempt to end the debate by control instead of allowing the debate proceed and so arrive at its conclusion.

 It has been held by many, for millennia, that man is the measure of all things. This is especially true in current dialogue on homosexual marriage. With reason, it is conjectured, intolerance and bigotry can be confronted and defeated. But reason always comes with its own baggage, even more than the variant definitions of secular.  Reason is a method, not a system of thought.

Incoherent Reason

The idea of the reason-driven life often, most often, lacks any coherent constraints or framework. With the practical ethic (the real framwork of this undefined thing called reason) floating somewhere between pragmatism and utilitarianism, it is easy to imagine a world where population reduction among minorities becomes a government program, where newborn children are left exposed to die (or are actively put to death), or where children have their brains sucked out, all in the name of someone else’s rights. A society with no moral constraint is a monster, as are those who promote and defend such behavior.

Reason also has no (for as a method it cannot have) definite teleology. As such it can only lead to tolerance when the reasoning person decides, arbitrarily, that tolerance is needed. It was reason that led to the intolerance of the Holocaust and the U.S. eugenics movement. The teleology of reason is at the whim of those in charge.

Reason as a criteria is also unfalsifiable. It is a term so broad that it can produce no mechanism which can be challenge. There is no measure for reason. Now, one might appeal to either European rationalism, or perhaps to Hindu ideals. But I have yet to find a Western secularist who is willing to push or throw a Hindu widow onto the funeral pyre in the name of tolerance. This is because the Western secularist still finds his moral home within the Christian ethic, no matter how hard they try to escape. That is their heritage and their inheritance.

This is not the common principle of tolerance in interpersonal matters. But the tolerance doctrine is a type of policy directive which intends to specify certain items of concern while ignoring (not tolerating) contrary opinions.  In the case of homosexual behavior we are told that the behavior is to be tolerated.  at the same time the proponents of homosexual behavior and marriage express an intolerance of any orthodox Christian response to their message. 

The intolerance of the homosexual proponents goes as far as to disallow religious content to the objection.  This exclusivity not only begs the question on its face but also creates an intrinsically histile atmosphere, thus stifling dialogue.  (That appears to be the the intent.)  This type of "just go away" or "shut up" attitude not one where teh Christian ought to be silent.

The tolerance doctrine is in fact misdefined.  It is merely a pragmatic, somewhat utilitarian, and altogether naturalistic world view that seeks to replace Christianity with its own theodicy.  Still, as a form of tolerance it is incoherent and as an alternate world view is it both intolerant and intolerable.

On Homosexual Marriage

In light of the failings of both reason and secularism as valid foundaitons for establishing homosexual rights such as marriage, we can now raise other foundation as suitable objections.  The question of immorality is certainly suitable, given the general public sentiments about the nature of marriage.

Though the homosexuality proponents have enjoyed a great deal of success in their public persuasion regarding "love" and their redefinition of "marriage" and "family" to include most everything.  But the discussion is far from over.  It takes little effort to show the meaningless of these arbitrarily broad definitions.  By appealing to classic definitions of these terms have maitain a simle historic defense of traditional marriage and at the same time show the incoherence of their new dictionary.

In a final, desperate appeal the homosexual proponent might become libertarian.  The quesiton of "no harm" is frequently raised.  This might be valid if we were living in a nation which was so libertarian.  but we do not.  Sexual morality is a part of state alws, and ought to be, to reflect the nation's religious constituency.  Were we also living in a religion-free society then the argument might find some other validity.  But again, we do not, so it does not.

Though that might appear arbitrary, it is not.  For public officials to promote immorality is a matter that the NT deals with (Mt. 14, John the Baptist v Herod).  For Christians to be silent on this would be inconsistent with the Biblical example.  (Going further, we ought confront sin in all areas of public life, irrespective of IRS intrusion.)

Conclusion

As arguments for homosexual marriage, the claims of secularism and reason fail.  Secularism fails because it is both vague and arbitrary.  Reason fails for its incoherents.  The remaining arguments of libertarian practice are both arbitrary and inconsistent.  Only a religious morality can be consistent, and the Christian position meets that criteria.

If this position amouts to bigotry, then I am also bigoted against a woman marrying a dolphin, borther marrying sister, polyandry, cohabitation, and so forth.  The inconsistency with the homosexual position is that the line between moral and immoral (if such a line even exists) is wholly arbitrary (for it can be nothing other).  The moral position has its support in Biblical revelation, and only that is consistent with human biology.