It's called recruitment and indoctrination.
Nature or nurture, I don't know which but I'm not sure they can recruit if by that you mean to change someone's sexual orientation. IMO, you either are or you ain't. What they want to do is normalize it, make it socially acceptable. They need to do that by the force of law because even liberals will mock them behind their backs. It's an anomaly, it can never be classified as normal.
Having said that, I have had a few friends over the years who are gay. They never told me they were gay and made no untoward advances on me but I know they are gay. They don't want the world to know and their secret is safe with me. I don't shun them as human beings because of it.