Heterosexual marriages have been the bedrock of societies for a very a long time now. As an atheist I do not have a particularly moral view of marriage but rather a pragmatic one as far as the state is concerned. If it could be proved to me that gay marriage was as stable as traditional marriage, and more importantly that gay couples were as capable as heterosexual couples, at raising children, then I would support gay marriage, if the opposite were true, then I would oppose it. Either way, my point of view is based on the utility of marriage and its effects, there is nothing ideological about it.
Before we consider whether gay marriage should be considered as equal to heterosexual marriage we should be mature enough to recognise that there is a rational reason to assume that it isn't. Most of our behaviour is evolutionarily determined. Women's behaviour is wired differently based on their evolutionary value and men's is also wired differently for the same reason. Loosely speaking women are evolutionary designed to be the bearers and carers of children and men the protectors and providers. This is not a culturally imposed state of being and it is not an assumed position from biology, but psychology. To support gay marriage and especially gay adoption is to make a fairly bold statement in the nature/ nurture debate. It is to imply that nature can be overcome and evolutionarily assigned roles can be 'learnt'. Homosexuality goes against our evolutionary programming to procreate, but this is not necessarily harmful. There are plenty of people who have vasectomies and use contraception which is just as unnatural as homosexual behaviour for the same reasons. Whether one wants to use language as politically charged as a 'disorder', or whether one wants to use the more benign 'alternative' we have to accept that in the arena of relationships, nature has set us a norm that homosexuality violates. The lines of what is acceptable seem to be incredibly obvious to those on the left. When someone decides during their teens that they are attracted to the same-sex it is considered something to celebrate, when someone decides they are attracted to children it is obviously seen as a disorder even if that person agrees to never act on that desire.
As far as my own views go, however reluctant I may be to say it, homosexuality is just as abnormal as paedophilia but it is not as harmful or equal as a disorder. Even though it may not conform to biological demands a relationship between two consenting adults should not be considered harmful or automatically threatening. A relationship between an adult and a child could never be a relationship because it could never have the child's consent and as such should never be compared to homosexuality. The same applies to those who ask if gay marriage advocates would support marriage between a man and a dog. And this is where I differ with most conservatives on the issue of gay marriage. Denying gays the right to marry is not going to stop them being gay, but it is going to deny them access to the institution that conservatives are supposed to believe in. The comparison to paedophilic 'marriages' or 'marriages' with animals is not a comparison at all because those are not marriages whether legal or not, in the way that gay marriage is between two consenting adults.
To come back to the first paragraph then, having listed some possible objections, I cited two reasons that conservatives are supporters of marriage. First, is the aspect of stability, the idea that commitment to another in a loving relationship over polygamy and promiscuity produces stable households and stable communities. In no way at all do I see a contradiction between these values and allowing gay marriage. Again however one wants to define the difference between gays and heterosexuals, they are not mentally ill, they are perfectly healthy individuals who are capable of living within caring and faithful relationships.
The second issue was that of parenting. While in caveman times the issue of parenting would have been irrelevant, in today's society gay couples can now have children through adoption (as one of a few ways). Someone that says that they are opposed to gay adoption, is by extension saying that it is better for children to be bought up with no Mothers than two of them. There is a lot of statistical evidence to support the notion that children brought up in foster care often end up committing more crime and contributing less to society, having not had an ideal upbringing. In regards to parenting I am one of those inclined to view parenting as a skill more than a biological trait. There are plenty of idiots out there having children, that make terrible parents despite having all of the 'biological equipment' because they simply have no clue about parenting. One of my big problems with a lot of modern feminism is its denial of the qualitative difference between the sexes, and as such I can't help but be slightly reluctant at breaking the evolutionarily created tradition of bringing up children with a mother and a father, which each have different roles. The point of adoption however, is that not just anyone can adopt children as there has to be a long vetting process for prospective parents to go through to see if they are suitable for raising children. It seems to follow to me that just as plenty of heterosexual 'chav' couples could do with some teaching in regards to raising children, that there is no reason why gay couples could not receive the same training, in providing the maternal care of the mother and the discipline more commonly associated with the father.
Either way, children's development is a very serious and nuanced issued as many psychology studies show if children are not brought up properly the damage to them psychologically can be irreparable. Therefore anyone giving an opinion on this issue who is willing to support the social experiment of allowing gays to adopt or choosing to deny children the opportunity to be adopted by gay couples and instead remain in foster care, should treat the issue seriously enough to look at the evidence provided by psychology that demonstrates the success or failures of same-sex upbringing and bring some stats to the table instead of treating it as an ideological issue which for the most part it isn't.