What can I answer to that ?

Homosexuality and the Bible

The passages that condemn homosexuality in the Bible (Leviticus 18:22, Romans 1:26) could be interpreted as condemning homosexual lust, in the same way that it condemns heterosexual lust, as it's discussing having gay sex out of wedlock, and having any sex out of wedlock is wrong.

On the other hand, the story of link shows that the Bible highly approves of strong male/male love and bonding. And while several homosexuality critics claim that their relationship was homosocial (strong bonds between men exceeding romantic love), however if this were true, I doubt that Saul would have been so upset with the relationship as it was.

Ergo, I'd like to think that the Bible promotes love of all kinds - including love between people of the same sex.

And even if you want to interpret the text as condemning homosexuality in all instances - love included - one has to remember that the Bible condemns several things, many of which are legal (gambling, drinking, adultery...), and many of which are downright ridiculous in this day and age (wearing clothes made of different threads, touching the skin of a dead pig, eating shellfish, wearing gold...). The Bible also condones things that are illegal, including slavery and misogyny.

Reliability of this response: All of these arguments come straight out of the mouth of a lapsed Christian with deep respect for Christ and his religion. I've read more of the Bible than some Christians I know who go to church every Sunday.

Homosexuality as Unnatural

As the graphic included in this answer attests, there are literally hundreds of animal species that engage in homosexual behavior, including our closest extant relatives, the chimpanzees and bonobos. Animals that form homosexual pair bonds (monogamous mates for life) include penguins, gibbons and swans.

In short, there is nothing unnatural about homosexuality. However, even if you want to ignore the evidence and claim that it is unnatural, human beings do not reject a concept or philosophy simply because it's unnatural. Synthetic fabrics, any tool or technology we use, even medical care and life-saving techniques are "unnatural" and yet we embrace all of those things. What makes homosexuality the odd duck out?

Reliability of Source: My information comes to me from two courses in biological anthropology and human sexuality at the university level.

Homosexuality and Population

It's admittedly true that if the world were entirely 100% gay, then there would be no way for us to reproduce without technology like invitro fertilization. However, contrary to popular belief, gays are not trying to take over the world. Conversely, those against homosexuality are trying to purge it from the world. [More in comments]

First, the Bible is not an ultimate source of ethics. Some may believe in the things written there, but not everyone is Christian, hence the biblical rules do not apply to all human beings. Saying that something is wrong, because a book says so is pretty naive, not to mention biased, if you ask me.
Second, according to the Bible, sacrificing your child is the right thing to do, but loving a person of the same sex is morally wrong. You really think that this a reliable source of advice on ethics?
Third, there is no possibility of everyone being gay, just like there is no possibility of everyone being blonde (pardon my somewhat lame comparison).
Fourth, ask her to give you at least one logical and rational argument proving that homosexuality is not natural. And if it is against nature, how is it possible that gay people exist and are born and raised in heterosexual families?

Haha, I love that argument: "If everyone was gay, the whole human race would disappear." There are ALWAYS going to be straight people. And we don't have to worry about a lack of breeders at this point.

But I found a quote today that may help explain stuff to Bible thumpers who are quick to condemn homosexuality.

"An engineering professor is treating her husband, a loan officer, to dinner for finally giving in to her pleas to shave off the scraggly beard he grew on vacation. His favorite restaurant is a casual place where they both feel comfortable in slacks and cotton/polyester-blend golf shirts. But, as always, she wears the gold and pearl pendant he gave her the day her divorce decree was final. They're laughing over their menus because they know he always ends up diving into a giant plate of ribs but she won't be talked into anything more fattening than shrimp.

Quiz: How many biblical prohibitions are they violating? Well, wives are supposed to be 'submissive' to their husbands (I Peter 3:1). And all women are forbidden to teach men (I Timothy 2:12), wear gold or pearls (I Timothy 2:9) or dress in clothing that 'pertains to a man' (Deuteronomy 22:5). Shellfish and pork are definitely out (Leviticus 11:7, 10) as are usury (Deuteronomy 23:19), shaving (Leviticus 19:27) and clothes of more than one fabric (Leviticus 19:19). And since the Bible rarely recognizes divorce, they're committing adultery, which carries the rather harsh penalty of death by stoning (Deuteronomy 22:22).

So why are they having such a good time? Probably because they wouldn't think of worrying about rules that seem absurd, anachronistic or - at best - unrealistic. Yet this same modern-day couple could easily be among the millions of Americans who never hesitate to lean on the Bible to justify their own anti-gay attitudes."
-Deb Price, And Say Hi To Joyce

You know what hurts?

When you suspect yourself to be Bi and your mom says the exact same thing your friend said. Right after you told her that you think that you're Bi.

I don't know what one can answer to such ignorant remark. People as narrow-minded as her (your friend) usually stubbornly dismiss any other opinion or point of view. It's sad, really. And it's painful for those who surround them, whether they are a part of the Gay community or not.

I suggest you'll never mention that subject again. If she continues spitting out comments like that, slap her in the face and tell her to open her eyes or shut up for eternity.