I won’t go into the full analytical treatment of it here, but under Propertarian analysis, marriage is a name for a corporation for the purposes of:
(a) reciprocal insurance of participant; and in modernity;
(b) power of attorney over one another, in the case of the incapacity of the other;  
(c) a political requirement that one eschew free-riding in one’s reproduction by requiring self-supporting production;
(d) a political incentive for males, who would otherwise act without incentive to preserve order (production); and
(e) a legal incentive to prevent violence over mates by treating the corporation of marriage as property that cannot be infringed upon (or rather, justifying violence if it is imposed upon.);
(f) and finally, a political strategy that forces the resolution of differences in reproductive strategy into the family, and conversely, to insulate politics from the differences in reproductive strategy between the genders.

Now, just so we are clear on whose interests are affected by these rules, (c) is meant to control female instinct to bear children of her choice, but to place burden of them on the tribe. (d) is meant to domesticate males so that they do not overthrow the existing order. (e) is largely to constrain females from destroying (a,b,c,d). So in this light, the institution of marriage is in large part necessary for the prevention of free riding that is natural for all females, and out of that prevention we obtain property rights, and peace.

Various societies construct and enforce these properties of the corporation. No societies do NOT suppress female parasitism, since societies that do not suppress female parasitism cannot survive competition with those that do. So while we tend to think in terms of suppressing the more visible threat of male violence, the central problem of producing prosperity is not male aggressiveness, but female reproductive free riding. This turns the criticism of demonic males on its head, such that short term male aggression and violence and long term female parasitism and gossip, are resolved in an equilibrium we call ‘marriage’.

However, once such an institution such as Marriage{a,b,c,d,e,f} exists, it is somewhat difficult to deny others other than male and female pairings, from access to the formation of their own corporations. My argument is that they are not equal to the purpose of marriage in all dimensions, but certainly: reciprocal insurance, common property, and power of attorney are rights we cannot deny people. In fact, I cannot imagine why we cannot create many such private institutions with however many members we desire. That seems to be something we can all benefit from – and which weakens the state, and state-corporatist power over us.

So what is important, and what I think is the proper subject for debate, is not this thing we call marriage that we argue in terms of traditional ceremonies and our own traditional intuitions, but instead, how to we grant (a) and (b) including community property if so desired, while preserving (c),(d),(e) and (f) – the prevention of these corporations from exercising political power with which to extract rents (parasitism), or by which they can export costs(parasitism).

Those of us who seek individualism in politics are wrong of course. We must construct law individually since only individuals can act, and be punished for action; but policy must be constructed familially, because the purpose of policy by any intertemporal judgement is familial: reproductive. So conservatives are correct in their attempt to preserve familialism in government. That is because the central problem of any society is the perpetuation of generations. So as long as any corporation is eugenic (meritocratic), and therefore possesses equal interests in government, then there is no problem with participatory government except that of class – and we can solve class conflict with houses of government established by property under one’s control.

WHAT DOES THIS MEAN
It means that we should articulate the properties of marriage as I have stated above, and state those which we grant and require of any corporation: we will defend these rights, as long as you hold to these other obligations.

If those are established, then by all means, one can form a private corporation for the purpose of mutual insurance at a minimum. And for the purpose of reproduction if possible. As long as one does not export one’s differences into the political sphere by engaging in rents (redistribution) or externalities (exporting of costs).

Under this analysis I see no reason to do other than encourage the greatest number of these alliances (corporations) regardless of constituency, regardless of gender, as a means of decreasing individualism and therefore incompatibility, in the production of policy.

All families have similar interests. All individuals have dissimilar interests. A family is the smallest possible tribe we can form: a man and a woman. And a jury (government) that treats all families equally save for differences in wealth is very different from a management organization (government) that attempts to calculate the impossible diversity of interests of individuals, when those interests are largely parasitic.

CLOSING
This may be a bit hard to digest, especially in short form. However, what I am advocating is that we have as many marriages as possible, and that we encourage as many forms of marriage as possible, as long as such a grant of property rights to one another is also met with obligations to one another: that we do not use government to compensate for our productive differences.

My view of Aristocracy takes the same approach to mankind: all tribes are the same, and we can cooperate as long as we do not engage in parasitism. If we do this, reproductive rates will solve our problems and man will evolve into a fairly equal creature regardless of race and gender.