Problem: According to some homosexuals, when Paul spoke against what is “unnatural” in Romans 1:26, he was not declaring that homosexuality was morally wrong, but simply that it was unnatural for homosexuals. “Unnatural” is used in a sociological, not a biological way. So rather than condemning homosexual practices, it is argued that this passage actually approves of them for homosexuals.
Solution: When the Bible declares that homosexual practices are “against nature” (Rom. 1:26), it is referring to biological nature, not sociological nature. First, sex is defined biologically in Scripture from the very beginning. In Genesis 1, God created “male and female” and then told them to “be fruitful and increase in number” (Gen. 1:27–28, niv). This reproduction was only possible if He was referring to a biological male and female.
Second, sexual orientation is understood biologically, not sociologically, when God said “for this reason a man will leave his father and mother and be united to his wife, and they will become one flesh” (Gen. 2:24, niv). For only a biological father and mother can produce children, and the reference to “one flesh” speaks of a physical marriage.
Thirdly, the Romans passage says that “men committed indecent acts with other men.” This clearly indicates that this sinful act was homosexual in nature (Rom. 1:27, niv).
Fourth, what they did was not natural to them. They “exchanged” the “natural relations” for the unnatural ones (Rom. 1:26, niv). So the homosexual acts were pronounced unnatural for homosexuals too.
Fifth, homosexual desires are also called “shameful lusts” (v. 26, niv). So it is evident that God is condemning sexual sins between those of the same biological sex. Homosexual acts are contrary to human nature as such, not just to a homsexual’s sexual orientation.
 Geisler, N. L., & Howe, T. A. (1992). When critics ask : a popular handbook on Bible difficulties (pp. 438–439). Wheaton, Ill.: Victor Books.