General Arguments Against Homosexuality
In all honesty, I've yet to come across a single valid argument against homosexuality or same-sex marriage. The concept of it being "unnatural" is false because it is, in actuality, a very natural part of life. It is not "destructive," no more than heterosexuality and traditional marriage is, because it is nothing but a unity between two consenting individuals. Any offspring of the homosexual couple (whether through adoption or a surrogate) have no "threat of becoming gay" because homosexuality is a non-intrusive sexual orientation. It is not an ideology, nor does it have any doctrines, postulates, or axioms to adhere to.
Homosexuality as a Sin
The second argument I've often came across is the claim that it is a "sin." Well, what evidence is there to support such claims? While I respect the words of the Bible as the religious scriptures of Christianity, I find it fallacious to use its texts as evidence because there is seldom evidence to support the texts themselves. For example, Leviticus 18:22 (KJV) clearly states: Thou shalt not lie with mankind, as with womankind: it is abomination. The issue, however, lies in the Book of Leviticus itself.
Leviticus was written by the Levites (specifically the priests), hence its name. The conflict resides in the fact that the entire book was more along the lines of religious commentaries and postulates as compared to the "Holy Word of God" that so many claim it to be. While there is no evidence to negate the latter claim, there is none to support it, either. Therefore, to support the belief that these priests—whom likely did not even claim it was the "Holy Word of God"—were divinely inspired is fallacious due to a lack of evidence and a failure to satisfy the burden of proof.
What if the Book of Leviticus was merely the written form of cultural and ethical views of the Levites? It's plausible that the Book writings were nothing more than a set of beliefs written down by priests after consulting its members about what the Levites are to believe. To put it frankly, the priests could have simply written in their own personal agendas and convictions, whether out of a desire for power or for political gain. The writings of the Levites are important historically, of course, but to glorify them as holy is an exaggeration.
The next most popular verses are those of 1 Corinthians 6:9–10 (KJV), which states:
 Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind,  Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God.There are two issues surrounding these verses. Firstly, the closest to any sexual acts it touches on is in regards to fornication and adultery. Now, fornication is another way of saying infidelity or sexual activity outside of marriage. This is a sin not exclusive to homosexuals; rather, it is simply a violation of the traditional marriage code of fidelity. Such a violation can occur between two heterosexuals just as readily as with two homosexuals (if they were to marry). Adultery is synonymous with fornication, however it denotes a slightly different meaning, more along the lines of sexual promiscuity. Again, promiscuity transcends all sexual orientations and preferences, thus invalidating it as a legitimate argument against homosexuality.
If that isn't enough, there is always the second issue: the verse that comes right after it...
 And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.Even if homosexuality is a sin, it has been "washed" and "justified in the name of the Lord Jesus, and by the Spirit of our God." Therefore, condemning something God already forgives makes you the Sinner because you are not following the "Holy Word of God."
The Bible Was Written by Man
Lastly (and perhaps most importantly) is this: every single holy scripture and religious text were human creations. The Bible, Qur'an, and TaNaKh were all written thousands of years ago by ignorant, borderline illiterate men who believed that the earth was flat and Jerusalem was the center of the known universe. A number of them were either exiles, fictitious characters for dramatic effect, or people whose words are questionable even to this day.
I do not say these things out of malice or blasphemy, but out of genuine sincerity. These men were, after all, just men and while the Bible does have some very valid and wise points, to claim it as inspired by divinity without any evidence of such inspiration (or even of the divinity itself) is, by definition a fallacy. That doesn't mean they weren't inspired by God; however, it's quite plausible that those men were just writing down folklore they remembered as a child and used it to represent something supernatural. That is called mythology.
The Validity of the Bible
There are over three different accounts of Jesus Christ's Resurrection from more than three different Disciples. No one knows which one is true—if any of them are—or if it was even the Disciples who wrote it. There is even evidence to support the possibility that the events in question were recorded hundreds of years after it occurred. This implies that they were passed down orally, thus allowing for misunderstanding and falsification to happen. Nonetheless, those are all seemingly different perspectives of the same event. How could all three be true? Are they not all the "Word of God"? That means that either God was wrong (or lying) two of the three times, or two of the Disciples (or whoever) who wrote down the events were wrong (or lying). Personally, I'd bet my money on humans being wrong and not an almighty deity.
The Bible is far from being "perfect." In fact, the original Holy Bible was about twice as large as the modern-day Bible. Before the First Council of Nicaea in 325 AD and the Roman-Catholic Church started banning certain books with accusations of "heresy" and "Devil's Work," there were many other books (e.g., the story of Adam & Lilith, the first wife before Eve, the Fall of Lucifer, and the Gospel of Judas). Many of those books were removed because they contained "too much knowledge" for the public to know. If the Church itself has been filtering its own religious texts since its beginnings, then what's stopping the rest of society from doing so?
The Bible has been translated, rewritten, and revised thousands of times. It's more than possible that some texts have been skewed for personal reasons. Even in biblical times, those in power were often corrupt, cynical, self-absorbed narcissists. Unfortunately, most of the ones in power were also religious officials, since theocratic rule was most popular and "God's Word" was considered Law. What, then, is it that exempts religious officials—priests, popes, and religious authors alike—from lying? Or manipulating? Or what about deceit and a lust for power? Is it just because they claim to be the harbingers of God's Holy Commandments? If so, then shouldn't every politician make such extreme claims? These are questions many religious officials and followers avoid (and with good reason).
Homosexuality is not a sin. It is not destructive, nor is it an "abomination." It is not inherently bad and the "sins" that could be committed by being homosexual can be done just as easily by a heterosexual. The only arguments against homosexuality can be found in one or more of three categories:
- Ignorance – The individual does not have enough information to provide a legitimate opinion. Thus any claims should be disregarded as invalid.
- Superstition – Whether in the form of religious beliefs or baseless delusions, the individual opposes homosexuality based off unfounded speculation.
- Biological Inefficiency – Since homosexual intercourse does not yield offspring, the reproduction and progression of a genetic line or heritage ends. A counter for such a claim can be that through a surrogate or donor, the legacy can be perpetuated. In addition to the latter, a lack of offspring can be beneficial if the genes in question are of poor quality, or if the threat of spreading a disease/illness (i.e., mental disorder or sexually-transmitted disease) is present.
Jesus did not once condemn homosexuality. His Apostles did and His Disciples did, all after His death. The words of Jesus' followers do not supersede His words, however, nor do they hold the same importance as His.
 One of the scribes came and heard them arguing, and recognizing that He had answered them well, asked Him, “What commandment is the foremost of all?”  Jesus answered, “The foremost is, ‘Hear, O Israel! The Lord our God is one Lord;  and you shall love the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength.’  The second is this, ‘You shall love your neighbor as yourself.’ There is no other commandment greater than these.”
 The scribe said to Him, “Right, Teacher; You have truly stated that He is One, and there is no one else besides Him;  and to love Him with all the heart and with all the understanding and with all the strength, and to love one’s neighbor as himself, is much more than all burnt offerings and sacrifices.”  When Jesus saw that he had answered intelligently, He said to him, “You are not far from the kingdom of God.” After that, no one would venture to ask Him any more questions. ~ Mark 12:28–34 (NASB)The greatest commandments never mentioned sexuality. It simply said to love God with all your being and to love your neighbor as you do yourself. Did Jesus exclude homosexuals from that love? Or adulterers? Or prostitutes? Or Atheists? What about people of another race? Or perhaps another nation or ethnicity? No.
"...You shall love your neighbor as yourself..."
Whether that neighbor is gay or straight; black or white; retarded or smart; rich or poor; male or female; friend or foe; communist, socialist, fascist, Nazi, or democratic; liberal or conservative; Republican or Democrat; introverted or extroverted... Regardless of who or what that person is, just as long as he is my neighbor, I will love him.