I'm very certain the parent meant it in an evolutionary sense that the individual will not pass on their genes to offspring - nothing to do with homophobia.
I’ve personally always wondered if there could be tribe-level selection for tribes with some non-heterosexual members.
But I also have personal experience, and I’ve met others who do as well, with life experiences that make me wonder if they could somehow affect sexuality. I know it might be presumptuous of me to consider the idea, but it’s only just an idea—one I usually keep to myself.
- there's literally nothing to stop a homosexual person from biologically reproducing,
- it assumes that the only value of an organism is in its Darwinian fitness (its ability to reproduce), which is pretty gross. I reject this assumption.
The parent appears to be applying this heuristic of value only so far as it implies a moral failure of homosexuality: it's not a typical measure of value. Humans value other animals more highly than this, without regard to whether they have reproduced.