There's no nicer way to say this but...

[kılıç_mehmet]

Thankfully, here, gay marriage is not even brought up by any political platform, or social institution. The people would certainly not stand by this offense against the nature of marriage.
How it directly affects *your* life, however, is like this. It really makes marriage something else than what it was supposed to be. Marriage was created solely to sanctify the union of two people, and protect the weaker party, which is the woman, financially or socially, if this union should be broken apart in any case at all. The union between two gays have never archived this social sanctity at any given time in human history save for few instances, where they still were not given the right to marry eachother.
Defiling the nature of marriage, is to defile one of the pillars of human society.
This is not exclusive to a religion or a culture. I can say that marriage takes up many forms throughout different parts of history, but the intent behind it remains the same still.
It affects your life directly by giving non-sanctioned unions the right to sanctity, and the rights to what was reserved to naturally child-producing unions, unions between a male and a female, the guarantee of future generations, and the marriage forms the concept of "the family" where children are supported by their parents until they form a home, a family on their own.

Allowing gays to enter "marriage", will probably change many fundamental concepts that are relevant to how society has progressed so far. I think that it will probably bring about the destruction of the family, and therefore, society.
Their (legal)unions should be given a seperate existence, and allow them to share property legally, and divide property accordingly on a breakup of any kind.

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Its about having a just society Mehmet. Surely having children isn't the only way a married couple can help it. And your argument fails because there are alot of hetero couples that choose NOT to have children, what you're gonna do? Force them to do that? As an hetero married guy, I don't think the fact that gays can marriage take any value away from my marriage, nor have any detrimental effects on me. But I do feel better knowing that 2 people that love eachother can have the same rights and protection me and my wife have.

Well, surely there are couples who choose not to have children. But I'm sure that these form quite a minority amongst the majority of couples who choose to have children.
Besides, I can tell you for a fact that it's rare that I've seen a marriage holding out for longer than 10 years without a child(I'm excluding straight couples who are physically unable to bring forth a child. These try other means to have a child, either via today's medical advancements, or by adoption, life is very hard on these people.). A child is like a glue, it forces people to handle their problems in marriage through means of dialogue, for the sake of the child. Wheras a marriage without a child is like a marriage for the sole purpose of sharing property. It holds no real relevance to society, although it still is socially sanctified, as being between a man and a woman.

I sincerely hope that when you have children, they don't turn out to be gay, not because of you, but because of my concern about that hyphotetical child having to deal with his own father's bigotry, and the whole suffering that would bring.

Well, that is what all fathers hope for, don't they. Have you ever met a father who said "Whoa, I hope that my child turns out to be gay!"?
By your accord, 99% of all fathers in the world are bigots and tyrants, who make their children suffer.

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But I say this for a fact, I certainly would be very reluctant to have ties with an openly gay child of mine. Just as I would cut off my ties with a child who has done things to publicly shame me, even though if I have taught him/her otherwise, I would cut off my ties with a child who practices his/her vices openly. Doing it secretly shows his/her respect to me, and my position in society. I also do things that I don't tell my parents. If I'd tell them that I have sniffed glue(socially not very acceptable), I'm sure they would be very upset. Besides, there is no need to tell them, as it's my own, private life.
Similarly, if I'd have a gay child, of whom I'm not aware of being one, and one that does not shame me by going around and doing things that are socially unacceptable, than he/she has respected the things that I've taught him/her, and taken up the burden instead of me. That is what I expect a child of mine to do.