Seven Flawed Arguments
Is homosexuality a sin?
Those who answer Yes employ seven flawed arguments.
1. God created Adam and Eve, not Adam and Steve. This argument says God will only bless marriages exactly like Adam and Eve, although God never makes that assertion in the Bible. For example, only two chapters after Adam and Eve, we discover a polygamous marriage in Genesis 4:19, on man with two women.
2. Genesis 19 proves that God destroyed Sodom for the sin of homosexuality. This argument collapses when we notice that although the Bible mentions Sodom 48 times, it never mentions homosexuality in the context of any of those 48 verses.
3. Leviticus 18:22 and 20:13 prove that God hates the sin of homosexuality. This argument ignores the context of "thou shalt not lie with mankind as with womankind." The context is shrine prostitution in worship of Molech and Ashtoreth, his fertility goddess consort, Leviticus 18:3, 21-22; 20:2, 3, 4, 5, 13. 
4. Matthew 19:3-12 proves that God only accepts male-female marriage relationships. This argument ignores a clearly stated exception for eunuchs, to Jesus' teaching, which He makes in vs. 11-12. Jesus lists three classes of eunuchs who cannot receive His teaching about Adam and Eve marriage. The first class He mentions is 'born eunuchs,' individuals born anatomically whole, who have not been physically castrated but who are not inclined toward heterosexual marriage. 
5. Romans 1:26-27 proves that God prohibits all homosexual relationships. This argument ignores the historical and religious context in which Roman Christians received Paul's letter. The issue for Paul and for God was prohibiting Christians from engaging in fertility goddess worship, (Cybele), not prohibiting committed, faithful, non-cultic same sex partnerships. 
6. 1 Corinthians 6:9 and 1 Timothy 1:10 prove that homosexuals cannot go to heaven. This argument ignores the fact that the words malakoi and arsenokoites were never used in the first century, with the primary or exclusive meaning of homosexual. Even anti-gay scholars like Dr. Gordon Fee admit that malakoi and arsenokoites were rarely if ever used to mean homosexual in the first century. 
7. Jude 7 proves that God destroyed Sodom because of homosexuality. This argument dies a well-deserved death when we point out that the Greek word for "strange" flesh is heteros, from which we get our English word heterosexual. Jude says the fleshly sin committed by the men of Sodom was heterosexual sin.
Had Jude or God intended us to believe that homosexuality was the sin of Sodom, they would have used the Greek word homoios, from which we get our English word homosexual. If homoios had been used, that would have been our textual clue that the sin of Sodom was homosexuality.
To answer the question then, No, homosexuality is definitely not a sin.