Gay is a physical and/or emotional and/or erotic attraction to a person of the same gender. This is similar to a definition I found on the online Merriam Webster dictionary that reads, "sexually attracted to someone who is the same sex."
Are people born gay? From various scientific and psychological articles, the general consensus is probably some are, and probably some aren't.
Do people choose to be gay? From various scientific and psychological articles, the general consensus is probably some do, probably some don't.
The condition, feeling, and experience of being gay is not sin. Anyone who is gay or has a close friend or family who is gay knows that many who are or feel gay wish they didn't. It's a difficult cross to bear, even in a permissive 21st century culture. Who wants to be the topic of every other media post and social media interaction?
I have friends and family with both unwanted same-sex attraction and others who welcome their orientation. I love them both and pray my friendships deepen.
Let's move on...
The condition, feeling, and experience of being straight is not sin.
Now, it is possible for straight people to sin. It is possible for gay people to sin.
A straight person is sinning if they engage in a sexual relationship with their sibling, no matter how consensual the action is done, even by adults. Even if they say they are naturally attracted to their sibling, it is still sin. Even if they say, they are born attracted to their sibling, it is still sin. Even if they find it pleasurable, say it is not harming anyone else, and take measures to prevent pregnancy...still sin.
Likewise, a straight person is sinning if they engage in a polygamous relationship, no matter how consensual. A straight person is sinning if they engage in an adulterous relationship, no matter how consensual.
These are moral positions held by most people for centuries. These are moral positions held by Christians for centuries because they are the plain reading of Scripture in both the Old and New Testament. We could add bestiality and pedophilia as other practices that are sin regardless of consent, feeling naturally attracted to, and arguing no one is harmed.
In a similar manner, because I believe the Bible is more sane, trustworthy, and sure than the changing waves of culture, I also think when gay people engage in consensual sexual activity they are also outside the moral bounds set by God and Scripture. This activity (not their condition or feelings or attractions) is what the Bible says is sin. (contrary to new attempts at interpreting the Bible, the Bible does not condone homosexual practice...see Kevin DeYoung's What Does the Bible Really Teach about Homosexuality?)
Throw in Jesus' warning that lusting sexually is also our hearts engaging in adulterous sin, every person reading this post is guilty before God. No one (NO ONE) is sexually whole. All are broken, struggle with seemingly natural desires that go beyond moral bounds, and thereby hurt others, hurt themselves, and sin against God.
Three responses are in order. We must first turn to God for forgiveness of sin through the shed blood of Jesus Christ. He alone can atone for our sin. He alone can give us the Holy Spirit to enable repentance from sexual sin and dangerous attractions outside moral bounds.
Second, we must continue to uphold moral truths for our lives (first! to avoid hypocrisy, see Matthew 7:1-2) and then for others as well. God's Word is light. We do no one a favor by consenting to the dangerous darkness that always hides the truth. Paul warns us in Romans 1 (a passage that mentions the sin of homosexual practice beside envy, greed, and gossip) that we should not approve of any moral transgression that keeps people from God and the truth.
Three, we must treat people engaged in sexual sin with love, respect, and honor because they are made in God's image. Yes, we can share the Good News of Jesus Christ and invite people to repentance. This will involve years of welcoming them into your home and life, lots of listening, and lots of prayer. Many will refuse to see what seems plain to you in the Bible, but don't forget, you too resisted God and re-read the Bible to make it say what allowed you to keep on doing what you wanted to do (and if you're like me are probably doing this very thing in some area of your life right now). Only God's penetrating and illuminating grace can free people from sin to see and live the truth. Only God saves, and praise God, He saves sinners like you and me.