I think it is time I weigh in. I will ignore the troll for the most part except for the following:
Of course any given set of parents might be as good as any other, but when you're dealing with policies on the scale of a country, you're going to have to deal with things in a statistical fashion due to the nature of the beast.
And when shown the statistics, there is no difference between gay couples and straight couples in their ability to raise children. As a result your argument is completely moot. Your notion of an ideal that must be encouraged exists only in your own mind. The interests of children are what the state has an interest in and the interests of said children are served equally well by both gay and straight couples.
(Why the fuck have we not banned or titled him yet? I would be happy to suggest titles to the admin staff if they just cannot think of good ones right now)
So I will repeat my position. Again. And not mention anything that compares same-sex marriage to any other form of marriage because people who discuss this issue are so defensive.
Protip: People do not like being equated to animals, child molesters, inanimate objects etc.
The problem is if these crazies (or any form of crazies) ever take power. And they claim that they will redefine marriage as being only a man and a woman because "They represent society, and marriage is whatever society wants". Thus, one of the strongest arguments for same-sex marriage becomes one of the strongest arguments against with.
Here is the problem with this line of argument:
The legal and moral justification used in our courts is not "Nothing says I cant do it!". First off, it is that our society has undergone several changes in the last few hundred years. Among them:
1) The concept of individual rights and equality and this concepts codification in law.
2) The tearing down of marriage as an economic and social merger between families for the efficient production of children and the securing of inheritance--Marriage now being an economic and social merger between two individuals who love and care for eachother so as to secure that relationship in whatever form they wish it to take.
3) Because of this, the state has no legitimate interest in barring marriage from same-sex couples.
This does not lead to the argument that marriage is strictly arbitrary in its definition. It is not. It is part of our ever evolving social contract and over time society has redefined what marriage is at its core (see point 2). This core definition now no longer bars same sex couples from participation, only the state does. The state, given point 1 has no legitimate interest in doing so and therefore the laws encoded ensuring individual rights kick in.
There are people who are genuinely polygamist in inclination, but it's probably always going to be inherently rare because even the smallest stable polygamist marriage needs three close interpersonal relationships, not just the one needed for a monogamist marriage. The odds of it working, and lasting, are inherently lower for that reason alone.
That is actually why Angurius mentioned this:
Polygamy: strongly associated with religious indoctrination and sex with girls who are not legal adults in this particular country. In principle, I do not disagree with the prospect that polygamous and polyandrous relationships could be legally recognized. However, I don't know if that's a good idea in this country anytime soon (I really CAN'T say, I haven't done the research).
That is the point. They are not stable unless there is abuse or coercion. Social polygyny (literally, multiple vaginae which yes is the proper plural for vagina) is very very rare in nature.
Disclaimer: I am skipping over most of the intermediary emotional bits and focusing only on reproductive conflict which drives the evolution of those emotional bits. Also consider this the disclaimer for evolution not being teleologically driven. It is just very hard to linguistically phrase it to avoid that implication.
Whenever the male puts in a high level of investment in a given offspring the partnership is almost always socially (though not genetically) monogynous. Note, this does not apply to organisms that defend a herem and their associated offspring like lions do. We are talking about when the male invests a high amount of resource based investment in the kids.
They are unstable because females do not want their male investing in someone else's kids (this is mediated through emotions like jealousy of course). The problem is that polygyny is often in the best reproductive interests of the male. In societies that permit polygyny (and polyandry is only noted in a few small human populations with an odd sex ratio, and it is usually brothers or close relatives sharing one wife--which is awesome if you are into incest porn) the males that engage in it are usually wealthy and of high status. He gains the most reproductive benefit through an optimization function that you can think of like this:
Disclaimer: This equation is very simple. I am using it for demonstration purposes only. Similar and far more detailed equations exist in the behavioral ecology lit, I just dont want to go through and find them right now because I am procrastinating the writing of a grant proposal.
K=R/M
Where K is the number of offspring he should seek to have
R is the total pool of resources available for investment in reproduction
M is the minimum reproductive investment that will be required per child. Depending on ecological factors there may be a tradeoff here also between the competitive ability of offspring (enhanced by high investment) and sheer number of offspring.
Functionally speaking a male can have a large number of children (Sperm are cheap, and the time it takes for a male to, in theory, impregnate someone is only a few minutes). Theoretically K can go from zero to infinity (although a max somewhere in the triple digits is more likely). Males seek to minimize M in order to maximize K. No guys, I am not saying you do not love your kids. Most of you have a number in the single digits. High level of investment in a few offspring means that your love gets concentrate in one or three kids. If you had 70 kids I can pretty much guarantee that you would be less attached to each individual child.
Females operate on the same equation, but K is constrained. They cannot physiologically have a large number of children, and there are costs associated with the raising and carrying of a child which increase M, thus decreasing K. Females thus seek to decrease their individual investment per child by seeking a male or other caregiver to assist in child rearing. They seek to maximize the investment per child by the male and thus will have a very hard time tolerating other females. You can see the problem. Also bear in mind that females have to trade off wealth, social status, and genetic suitability in their mate choice criteria. This will be important later.
Under certain conditions the tradeoff is such that it is better to share a male if the options the female has to choose from are low. For example in cultures which are resource poor but with a high variance in resource availability per male, sharing a high-status wealthy male may be better than the alternative of being in a monogamous marriage. Under such conditions polygynous marriages can be stable without the dissolutive effects of female-infighting and jealousy and the requirement that males engage in abuse and coercion. There are infidelity problems however, because the high status or wealthy males may not be good genetic partners. This creates a tendency toward cuckoldry, and thus males engage in abuse for that reason. In order to increase the risk or decrease the benefit of cuckoldry and thus avoid wasting resources on a child which will not contribute to his fitness.
In western cultures however, these conditions do not hold. A male seeking to monopolize as many females as possible generally must use coercion to keep a polygynous marriage together. This is why the only examples of large scale (read: not statistical outliers) polygyny exists within polygamous cults like the FLDS, which use forced and arranged marriages.
As a result the state and society at large have a legitimate interest in preventing these relationships from being officially sanctioned. This is true for another reason. Polygyny when it is permitted can be reasonably predicted to be preferred by any male who can reasonably attract more than one female. This will create a bias in the operational sex ratio in the population as females are removed from the pool available to single but otherwise eligible males. Thirty year old unmarried males are frustrated males. Frustrated males are dangerous. Competition for mates will increase, and sexual displays in humans tend to take the form of high risk behavior as an honest signal of male suitability. As an example of this we can look to males in urban slums within the united states. Resource availability is poor, and females emphasize the non-wealth part of their mate selection, preferring males of high genetic suitability and social status. In order to display the former and secure the later, males will engage in high-risk behavior. Namely crime, often violent crime. They will also do this in order to secure the resources necessary to provide additional incentive to potential mates. Yes you read this correctly. I am postulating that the subconscious reasoning for a lot of the crime that takes place in poor areas is the attraction of mates.
If this is true, then the state has a further interest in prohibiting legal polygyny (and yes, Polygamy is almost always polygyny, the notion that both will occur at equal frequency is not born out by history, anthropology, or biology. When the social and biological sciences agree, it is generally correct). The prevention of crime.
If you would like, I can also go into a high level of detail about how allowing polygyny may also lead to higher levels of background inbreeding.
The state incentive to minimize incest between close relatives is also significant. First is because there is almost always a power disparity which makes the relationship abusive. The second is the strong possibility for flipper babies due to inbreeding.