There sure seems to be a lot of... well ignorance around here. Not that it's necessarily a bad thing, but just something to point out. What we have here is a case of someone genuinely wanting to discuss a controversial topic. Be that as it may, I think some feathers may have been unintentionally ruffled.
Let's start off with this, "God created man and woman." While this is true, it certainly misses a very important subject. Around .5% of the human population, for as long as we have been around (200,000 years some state) has been born intersex. This means that they may have been born with an extra X or Y chromosome or have an androgyne deficiency etc. Whatever it is, it means that these people (around 1.7 million Americans) are neither male nor female. And you may be surprised to learn that Jesus actually acknowledges this when he discusses marriage in Matthew 19:12.
"For there are eunuchs who have been so from birth, and there are eunuchs who have been made eunuchs by men, and there are eunuchs who have made themselves eunuchs for the sake of the kingdom of heaven. Let the one who is able to receive this receive it.”
Now that the silly notion of all people fitting into one or two sexes is out of the way, let's focus on the actual point here. Notice, OP stated that he does not have a problem with homosexual marriage. Which, whether you agree with it or not, you must deal with the fact that (I am speaking from an American point of view) that we live in a country that is not 100% Christian, and we cannot expect to impose our view of marriage on non-Christians from a legal perspective as much as we would not want Muslims banning alcohol or Jews banning shellfish. Turn the tables and you see the absurdity here. After all, we Christians believe that divorce is also reprehensible in the sight of God (I wonder how many of you are divorced, or remarried even), yet we don't have anyone campaigning to make divorce illegal in our country. No, and why? We respect the rights of those who do not follow the same beliefs we do. We are secular after all. Let's keep our government that way.
And finally, evolution. I honestly... honestly get tired of this over and over again. Let me get started by stating that the Big Bang Theory, which some of you think is an atheistic attempt to prove the existence of the universe without God, was invented by a Catholic Priest. That's right, Georges Lemaitre was a priest, physicist, and astronomer, and was actually RIDICULED for the Big Bang Theory. Why? Because the very idea of the Universe having a beginning was considered TOO theistic for the scientists of the time. Einstein went as far as saying, "Your calculations are correct, but your physics is atrocious." The common idea in the 1910s was that the Universe had simply ALWAYS existed and hence, did not need a beginning, nor a creator. Lemaitre comes along and causes a paradigm shift in the field of physics and cosmology as huge as the theory of Evolution was in biology. So there you have it. Big Bang Theory=Theistic Science.
And now what better way to segway into the big spooky monster of... Evolution. Did you know that the Catholic Church accepts it as a genuine form in which God created life on Earth? Bet you didn't. Did you know that Francis Collins, head of the Human Genome Project, is an evangelical Christian. Probably didn't know that either. But what about George Ellis (Cosmologist), John Lennox (apologist, Oxford Mathematician, Philosopher), Alister McGrath (Theologian, Philosopher of Science, Microbiologist), and William Lane Craig (Philosopher)? Yep. They all accept evolution. But how? Simply because it has no bearing on the salvation of anyone involved and is totally within the realm of God's power to do so. The Bible is NOT (I CAN'T stress this enough) a text book. It is a collection of books compiled over thousands of years consisting of: history, poetry, songs, parables, letters, prophecy, apocalyptic imagery, and much much more. Is evolution compatible with Christianity? MOST CERTAINLY. Imagine God trying to explain amino acids and DNA to the authors of Genesis in 1200 BC. You would have simplified it too. Genesis tells us who God is, what he is like, and provides a preface for how our relationship with Him works. Could it have literally happened in 6 days? Sure, why not?
But what are the implications of that? God makes everything look old, billions of years old, adds fossils, puts clues in our DNA, gives us everything we can see to make it plain to us that the Earth is not 6,000 years old to... trick us? That doesn't sound much like the God we worship. Nowhere close. Creationism has the theological problem of painting God as a charlatan who makes us think the world is older than it really is... for no apparent reason. Think about that. Jesus taught in parables to make things easier to understand. When it comes to the creation of the Universe, and your audience is a group of people who have been in slavery and wandering in the desert for 40 years... they don't care about DNA. They certainly don't care about the age of the Earth (something the Bible NEVER states). What they care about is how God has led them to this point and where he goes from here.
Please feel free to respond. Thank you.