To sin means to choose against the Will and Laws of God.
Same-sex love is sinful.
Therefore, same-sex love is a choice, i.e., a lifestyle.
If same-sex love is not a choice then it cannot be a sin. Thus, the importance of the “gay gene" for some people.
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Consider the sex live of bonobos. Not every animal has a sex life. Only those that copulate for reasons other than procreation can be said to have sex lives.
An alien anthropologist studying human sexual practices without the benefit of understanding human speech would very likely dub homo sapiens the “horny animal.”
Someone (Freud I think) said “We are all perverts.” We desire sex independently and far in excess of procreational needs. Orgasms and release from sexual tension are frequently achieved through manipulation of genitalia without any possibility of procreation. This is one benefit of tool use and opposable thumbs.
Even the Christian crazies who strive to only have sex for procreation still have sexual wants and spontaneous physical reactions to the presence of an attractive member of the opposite (and sometimes same) sex. For instance, absent specific olfactory stimuli from a bitch in heat a male dog does not copulate. Nor does a bitch not in heat. Human beings always seem to be in heat. Sinbad said, “If we ever encounter a space alien, no matter how ugly, some guy will want to have sex with it.”