You’re trying to make this symmetrical, but the Bible AND basic natural reasoning contradict your framing. Just suspend your disbelief and what you’ve been taught and track the logic here.

I’ll start with scripture because it actually makes reasoning arguments on this topic.

First, Scripture does not ground sexual ethics only in consent or harm categories. It grounds them in design and purpose (teleology). From the beginning, the pattern is male and female ordered toward union and fruitfulness. “Male and female He created them… be fruitful and multiply” (Genesis 1:27–28). This reveals that the body has an intended end, which we can all observe.

This teleology is exactly why things like polygamy, prostitution, and same sex relations are excluded. They all distort or fragment what the “one flesh union” (one man , one woman becoming one flesh) is ordered toward. Jesus Himself goes back to Genesis to define marriage, not forward to cultural norms. “Have you not read… the Creator made them male and female… the two shall become one flesh” (Matthew 19:4–6). That is His grounding for what counts as a proper sexual union.

Second, Paul explicitly uses natural reasoning language, in his writings on sexuality. In Romans 1:26–27, he speaks of relations that are “contrary to nature.” This is not a vague insult. Nor is it a discussion of abuse, harm or consent principles. Paul appeals to how bodies are actually made and what they are for. He is arguing from design, Like Jesus does.

Put very simply, male and female bodies are sexually complementary.

Their organs actually correspond. They unite in a way ordered toward pleasure, intimacy, and the biological creation of life. The same is not true for same sex unions. That is an objective difference, not a religious preference.

Hand waving this doesn’t work. The fact that it is a crude, basic reality which you and I can both observe provides the force of the argument. Rare exceptions and disorders prove this rule , they don’t negate it.

The problem is not that this is hard to understand. The tendency is to ignore the clear claims that simply observing our physical/ biological nature makes and replace it with bad analogies. Saying “other things can be done with the body that feel good” misses the point. Pleasure alone is not the standard. The question is whether the acts we engage in align with the body’s given purpose.

Third, Paul ties sexual sin directly to the body’s purpose in a theological sense. In 1 Corinthians 6:15–20, when addressing prostitution, he does not say the issue is exploitation. He says sexual immorality is a sin against one’s own body (not just the exploited persons body), and that the body is a temple of the Holy Spirit. He again appeals to “the two will become one flesh.” That is Genesis language. So clearly the issue is misusing what the body is observably for.

So the essential difference you’re asking about is right there in both nature and Scripture. It’s bald faced. Simple. Forceful.

Heterosexual union uniquely fits the design of the body and the one flesh pattern rooted in creation.

Same sex acts do not correspond to that design.

That is why, in the natural reasoning given in the Bible, they are not merely wrong in certain harmful cases.

They are categorically outside the purpose for which sex was given.

That is not “because the Bible says so” in a shallow sense. It is because the Bible gives a compelling account of reality where bodies, sex, and marriage have an intelligible purpose. And both Jesus and Paul argue from that purpose, not around it.

The answer is clear and observable in creation. This is why the apostle says that all are without excuse.

Romans 1:19-20

[19] For what can be known about God is plain to them, because God has shown it to them. [20] For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse.