I've encountered three common arguments against homosexuality, and they're all total bunk.
1. Homosexuality isn't natural.
We've cruelly butchered our own sense of sexuality, and blinded ourselves to sex in nature. Many other species masturbate, and some thought to be monogamous also cheat. In some species it is distinctly normal for some of the population to be gay at least some of the time. This includes primates such as chimps.
2. If everyone was gay, the human race would die out.
I'll bypass the rather tempting "so what?" in favor of a much better argument:
There will never be a time when everyone is gay. It seems that there are gay genes, but heterosexual genes maintain an average majority. Even if there were a gay majority, gay people do not necessarily lack the urge to raise children, so the only effect is that there would be fewer of us, because every child born of a lesbian would be planned.
3. It's just not right.
Homosexuality was defined as a mental illness for decades, because gay people exhibited less stability in relationships and higher suicide/mortality rates. This was a reflection of their treatment in a society that assumed then thought they were ill. Now it's more acceptable, there are gay people that exhibit characteristics of psychological health and manage long term relationships.
With regard to gay effeminacy, it's just unfortunate that gay culture is associated with homosexuality. I know a few gay people who are not "gay" in the clichéd sense at all (which AFAIK is pretty much what's on show at pride parades).
One of them loathes gay culture with a passion. I agree with him on that, but think it's about equal in superficiality and mindlessness to the vagaries of fashion and herd mentalities that you'll find pretty much anywhere, regardless of sexuality.
I also know a gay couple who've been together for 20 years. When I first met one of them, I had no idea whatsoever he was gay.
I've met awful gay people, awful straight people, and awful bi people. I've met brilliant ones too. Sexuality has no bearing on how good or worthy you are as a person.