Then base your ideas on reality, not ideology. Homosexuality is, at best, an evolutionary dead end, a failed mutation that crops up in a tiny portion of the population.
The purpose of sex in the evolutionary sense is procreation, that is, the perpetuation of the species. Homosexual sex CANNOT perpetuate the species. Period. Therefore, homosexuality is counter-evolution and in no way something to be encouraged for the good of the species.
There you go. A non-religious reason why we should not be supporting or encouraging homosexuality.