The whole issue of a “gay gene” is meaningless. Whether same-sex attraction is caused by a gene, or hormones, or trauma, or targeted radiation beams from flying saucers makes absolutely no difference.
What the Catholic Church teaches—and all Christians once believed—is that all deliberate seeking of venereal pleasure is grave matter, except in mutual acts between husband and wife which are in themselves capable of transmitting life.
Those who insist that the issue is that “people choose homosexuality”—IF they mean that people with same-sex attraction choose to have same-sex attraction—are creating a distraction, and undermining Christian moral teaching.
Because: Those who HAVE same-sex attraction know that such people are fools. If Christian moral teaching DEPENDS on the notion that SSA is CHOSEN, then those who know they DID NOT CHOOSE IT are perfectly entitled to reject Christian moral teaching. In fact, that is a principal reason that so many DO reject Christian moral teaching—because they THINK the Christian view is that they chose to have SSA.
SSA is nothing more than one more method by which a person is willing and/or ready to relieve an urge for sexual release.