It is a fair question and you deserve a non-confrontational answer.
1. Not everyone believes in a Heavenly Father or God. Different religions have different accounts of human origin, which can accommodate LGBTQ, to say nothing of science itself.
2. Speaking of science: There is a lot of “gender-bending” in the natural world. Lionesses with manes, seahorse males who get “pregnant,” etc. Behavior and sex characteristics that do not quite fit a male/female binary for all sorts of reasons. Who’s to say therefore that LGBTQ is not “natural”? Obviously, for those species, it is. And if LGBTQ-type behavior is observed in other species, then why not ours?
3. Finally, freedom. Regardless of religion, regardless of science, people are happiest when they are FREE TO DEFINE THEIR OWN DESTINY. Even if you personally believe LGBTQ unnatural, the alternative of forcing people to identify as something that they’re not is intolerable in a free society that respects human rights. We let people be “wrong” about other stuff in life that we might disagree with, without invalidating their existence.