How can gay marriage destroy the family?

It cannot and does not. Religious objections are nothing but bigoted stupidity.

Fundies think gay marriage increases gay kooties and they are deathly afraid of gay kooties.

It can't. If you force gay people to marry members of the opposite sex, they're going to be miserable and possibly cheat with the same sex anyway, so it's not like they'd be leading a "normal" straight life even if it appears so on the outside. I definitely do see social value to the nuclear family, but allowing gay/bi people to be themselves and accepting different types of families does not threaten that. If anything, giving them the option to be their true selves is better because there will be much fewer sham marriages and associated consequences.

Like everything else they say -- it's unfounded, unsupported HORSECRAP.

Who says their BS CLAPTRAP the loudest and most often?

Religious CLOSET CASE GAYS. Oh -- hi there, nightmare...

Everyone inherently knows that homosexuality is immoral and unnatural, and the only way to suppress this inherent knowledge is by normalizing homosexuality and attacking any and all opposition to it. The best way to normalize homosexuality is by placing gay marriage/same-sex marriage on an equal plane with traditional opposite-gender marriage. Romans 1:18-32 illustrates this. The truth is known because God has made it plain. The truth is rejected and replaced with a lie. The lie is then promoted and the truth suppressed and attacked. The vehemence and anger expressed by many in the gay rights movement to any who oppose them is, in fact, an indication that they know their position is indefensible. Trying to overcome a weak position by raising your voice is the oldest trick in the debating book. There is perhaps no more accurate description of the modern gay rights agenda than Romans 1:31, “they are senseless, faithless, heartless, ruthless.”

"According to Christians and Muslims, gay marriage is going to destroy familes." A sweeping generalization. Not ALL Christians and Muslims believe that. And it makes no sense. Religious belief aside, marriage is a stabilizing agent.

History argues against gay marriage. Modern secular psychology recognizes that men and women are psychologically and emotionally designed to complement one another. In regard to the family, psychologists contend that a union between a man and woman in which both spouses serve as good gender role models is the best environment in which to raise well-adjusted children. Psychology argues against gay marriage. In nature/physicality, clearly, men and women were designed to “fit” together sexually. With the “natural” purpose of sexual intercourse being procreation, clearly only a sexual relationship between a man and a woman can fulfill this purpose. Nature argues against gay marriage.

It makes no sense at all.

Only a closeted gay would believe that given a free choice, everyone would choose to be gay. Straight people would never make that assumption.

Any evidence to back up your claims?

thats not a common argument against gay marriages by christians and muslims. I disagree. Sources?