The logical argument

Firstly to clarify this is "The logical argument against same sex marriage" and most definitely not "the logical argument against homosexuals; the practice of homosexuality and/or any opposition to traditional marriage".

What we plan to underline is why two members of the same sex should not gain the legal, financial and social equality to other marriage types. Firstly we must clearly and concretely define what we are speaking about.
The two words that come up are "Marriage" and "Same-sex/Homosexual". Now we shall look at "marriage" and define what it means in this instance.

Marriage is a social institution almost as old as first human civilisation. It has existed in many forms, in many different cultures, some group, some polygamous, and very rarely same sex, but the overwhelming majority in all cultures is the "traditional" marriage of one man to one woman. When you consider how old the tradition of marriage is, it must be clear that marriage is an important and universal concept. Originally marriage between a man and a woman was a contract of sexual exclusivity in order to ensure paternity of any offspring. In short a behaviour so that a man will know that any children his wife bares are biologically his own, of course the woman will already know. We see here that exclusive marriages are a behaviour that ensure a man will spend his time caring for his own biological children and not those of another man. Biologically this is hugely beneficial and time saving for males that previously needed to defend jealously defend any woman which whom they had mated. Also the woman ensures a male that will protect and care for her young. Both parties win in this situation and so the institution of heterosexual marriage was seen as very important and bound into culture and religions of the world.

Here's a dictionary definition to use later on. Marriage: "a behavioural contract of life-long sexual exclusivity, between two or more parties, in order for a male to ensure paternity of young born to a female." We'll come back to this a little bit later.

Secondly we must tackle the homosexuality part. Homosexuality has also existed for a very long time, also somewhere around the beginning of civilisation, however this was considered, until recently, as an activity rather then a lifestyle or predisposition. Ancient Greeks seemed to show strong preference for any extended period of time. Now let us look at the word homosexual and define it. Merriam Webster defines it as so; "of, relating to, or characterized by a tendency to direct sexual desire toward another of the same sex". Though there is still some debate whether homosexuality is a conscious choice, We will use the addition of "sexual desire, and acting upon these desires, toward another of the same sex".

So now we have two behaviours. Marriage and homosexuality. Both aren't physically compatible as we have noted them, as marriage requires one partner to bare children. A person can only act in both if we remove "in order for a male to ensure paternity of young born to a female". Are two statements read as follows;
"A behavioural contract of life-long sexual exclusivity between two or more parties."
" A tendency to direct sexual desire, and acting upon these desires, toward another of the same sex."

Now both of these definitions are possible for someone, so inclined to simultaneously accomplish.
Given the base of liberty and freedom of choice in most western constitutions, neither of these actions effect anyone outside of the marrying persons and cannot be objected against, so problem solved? Sadly not, this is not considered a "gay marriage" by those advocating for it's legalisation. Rather a long term gay sexual relationship. In essence Gay marriage has been legal in most western countries for many years, and yet there is still a campaign to "legalise gay marriage".

To understand this continued effort we must once again alter our aforementioned definition of marriage. What is being campaigned, debated and legislated for is civil marriage rights equal to that of Heterosexual "traditional" marriage. This includes but is not limited to: prison visitation rights, will and inheritance rights, tax deductions and incentives, social acceptance and normalisation and legal recognition of union. Adoption right by same-sex couples has been purposely omitted as we see it as a different issue.

Some issues listed above should be compatible with constitutional rights, effecting no person outside of the marrying persons, such as visitation rights and inheritance rights. A problem is caused with Tax deductions or incentives, Legal recognition of union, and social acceptance.

Tax deductions and incentives for "traditional" married couples were introduced as a way to encourage couples to marry and make a stable base for raising their biological children. However if this is applied to a same-sex couple, discounting the possibility of adoption, the tax deduction or investment is fruitless. All tax payers would then be effected by the act of same-sex marriage. They must have the right to object, just as any taxpayer can object to any governmental tax reduction or spending initiative.

Furthermore social acceptance is no something any amount of legislation or lobbying can change. It is the collective opinion of a populous on a subject, which must be left to the individuals free will. Should a governmental body act in any way to influence the opinions of its people, positively or negatively, it would be an offence to the free judgement of it's citizens and unbiased nature of any constitution.

The third and final point Legal recognition of Union is difficult as it brings us back to one of our original points and the exact definition of homosexual. What is it to be homosexual? Nature or Nurture? Is it something that should be something governments or organisations do to encourage? Do we accept it as equal in all aspects or differentiate the clear deviations from the norm? These are all very difficult moral and philosophical questions that each person can come to their own answer which in any case is philosophically right. Therefore only by referendum can any legislation on the union of same-sex couples be accepted as valid and lawful.

Now I hope you can see that there is logical non religious reasoning against same sex marriage, even if it has not changed your mind maybe you can think and act differently in the debate on this issue. As always, more information, more knowledge and more opinions, are immeasurably beneficial to intelligent debate that furthers society.