God defines marriages as between a man and woman in Genesis 2. Humans cannot override God's definition.

Separation of church and state means the State can't establish an official religion or force anyone to practice a religion. It doesn't indicate that the legal basis for the State's laws can't be a religious text. If that was the case, murder would be legal because "Thou shalt not kill" is violating separation of church and state. God's Law is the only reliable determiner as to what's moral or immoral.

That's actually why I'm alright with the idea of the government not even having a definition of marriage. It incentivizes people to get married for tax breaks or other incorrect motives. But if we are going to have a state, it shouldn't encourage harmful activity like homosexual behavior.

I agree that we should love our fellow human beings. That's why I oppose state-endorsed homosexuality. It's dangerous to everyone involved, and as someone who values human life, I can't endorse it.

If marriage has no higher basis than human contract, why should the state be involved in defining/rewarding it? Why should the state be incentivizing it with tax breaks and other benefits? And Genesis 2 actually has several relevant passages to U.S. law: intrinsic human worth, Sunday as a day of rest, gender equality, and the innate dark nature of humans. Removing its influence leads to a reductio ad absurdum.

Marriage has always been a religious matter, long before the modern state existed. When it gets turned into a civil issue, people are incentivized to marry for selfish reasons (tax breaks, financial convenience, etc.) Marriage should be based on mutual selflessness, which doesn't allow for homosexuality.

Any time someone forbids murder, they're "enforcing religion on someone else" (Thou shalt not kill). Religion isn't based on individual preference. Their choice of religion may be, but religions themselves are based on truth or falsehood. Separation of church and state means you can't force someone to practice your faith, not that a society's laws can't be inspired by religious ethics. When you take that away, you're left with the state atheist governments we saw in the USSR and China.

Separation of church and state refers to not establishing an official Church of America or forcing anyone to adhere to a faith. It doesn't indicate that religious philosophy/ethics can't serve as a foundation for our laws. If that's what it meant, we'd have to legalize murder, because making murder illegal would be violating separation of church and state (Thou shalt not kill).

It may not affect me, but it does affect the people in the relationship. Homosexuality if physically and mentally harmful, even when consensual. The government shouldn't encourage people to harm one another and call it "love."

The reason that rights are inalienable is because God has instituted them as such. The rule you're calling "fictitious" are what created the society that allows you to call them fictitious. Homosexual behavior is biologically harmful, and physical injury does violate another person's right to physical safety.

Agreed that for the sake of persuasion, we need to approach this issue from multiple angles. If I remember correctly, the question asked for my "best counterargument," and in light of ultimate Truth, God decreeing something is the ultimate counterargument. But to your point, I've emphasized the harmful physical effects of homosexuality (and therefore its violation of human safety) in some of my other replies.