One way to look at it: humans pretty much always form a social group. All over the world, people gather together for the common good: for mutual defense, to support people with specialized skills (you wouldn't want to waste a cook's time with farming, and vice-versa).

Having lgbtq+ people in your family is a create way to have additional adults (who can do lots of things) without the burden of additional children. Hence, any group that welcomes their lgbtq+ family will be a stronger group.