They always bring up the Bible as their first argument ("God created Adam and Eve, not Adam and Steve"). Of course, while they are happily quoting Leviticus to condemn gays, they are ignoring pretty much all the REST of Leviticus. They also ignore the fact that "traditional" marriage in the Bible included such wonderful nuggets as husbands being allowed to stone their wives to death if they discover on the wedding night that they weren't virgins.
"Traditional" marriage is very much an antiquated thing that we've (mostly) evolved away from. Yes, in some cultures we STILL have arranged marriages (the pre-arranged marriage seems to be the plot device of MANY current Bollywood movies wherein the "modern" lovers have to defy the traditions of their families (ala Tevye's daughters who all defy their family's traditions in "Fiddler on the Roof")). However, that's no longer the norm in modern Western society.
Women used to be the property of their fathers until they married and then they became the property of their husbands. Traditionally, a dowry was paid to the family of the father to "buy" her from them. Yet, women weren't allowed to own property of their own (if their husband died, she along with any of his belongings usually went to his brother).
Nowadays, women are "equal partners" of their husbands and are allowed to choose their own fate (though, I'll bet there are many of the same people who are against gay marriage who also would like to go back to "traditional" women's rights). However, we still have the "ideal" of the nuclear family from 1950s television: the husband brings home the bacon, fixes the car, takes out the trash, mows the lawn. The wife is a stay-at-home mom who vacuums the house while wearing pearls and has dinner ready to go on the table when her husband comes home (as she hands him his pipe and newspaper), and does the dishes/laundry and sews the kids costumes for their school play.
We STILL force gender role toys onto our children. Girls get Barbie, dress up clothes, play kitchens and baby dolls. Everything is pink and princesses. Girls are taught to aspire to shop, date boys and be pretty (look at such girl toys as "Mystery Date" and "Mall Madness" as well as the awful new "pink"/"girlified" board games from Hasbro, exclusively at Toys R Us). Boys get G.I. Joe (still a doll with lots of outfit changes and accessories, but we call him an "action figure"), sports equipment, guns, cars, etc. They get board games like "Risk" and "Battleship" to make sure they are primed for war and aggression. Most fathers would blanch at the very idea of giving their son a play kitchen, yet on national television we're obsessed with Emeril Lagasse/Mario Batali/Bobby Flay/Masaharu Morimoto/Wolfgang Puck/Jaime Oliver/etc.).
If gays get married, there are two people of the same gender. If two men are married, does that mean that two people are mowing the lawn but neither is doing the dishes? If two women are married, does that mean that all the laundry is folded but there's no one in the house who can kill a bug?
This is why I think that one of the fears is that gay marriages will mean that we as a society will have to start abandoning our gender stereotypes for everyone. THAT's how gay marriage threatens straight marriage. Husbands are going to have to put dinner on the table for their wives who earn more than them in the marketplace. CHAOS!!
While on the subject of gender roles, one of the less-reported problems we are facing with the fights against gay marriage is the rights of the transgendered. Once we allow gays to marry, gender will not bar any two adults from getting married, regardless of what their birth/current gender may be. I've read couples that were originally composed of a man and a woman being dissolved/ignored when one partner has gender reassignment surgery thereby rendering them a same-sex couple. I've also seen opposite sex couples barred from marriage because one member of the couple was once the same sex as their partner. You can't have it both ways.
There are still people who discuss "family values" and debate that marriage is about raising children (and having traditional gender roles to raise those children with). There is no discussion, seemingly, about heterosexual couples who have no children (and don't plan to have any) or couples who include women beyond their child-bearing years being barred from marriage. These people say repeatedly "a child needs both a father AND a mother in it's life". That's all wonderful, but what about the many single parents out there? Many did not CHOOSE to be single parents.
What about the many kids out there growing up in a non-traditional family (one might say that my being raised by my grandparents after my parents' divorce placed me in that category)? Back when I was a child, I was the first child in my class with divorced parents (I wonder by my treatment by my first grade teacher if I might have even been the first in that SCHOOL). I remember when we would be doing art projects for mother's/father's day and my teacher, in 1974, not being entirely understanding about the fact that I didn't make the construction paper cards for my parents but for my grandparents. I can't imagine just how much harder it is on children today who are being raised by gay parents (who are unsanctioned by their state). Because, marriage certificate or not, there ARE gay parents out there. Not allowing us to get married isn't stopping us from adopting children and barring us from adopting children (I'm looking at you, Florida and Arkansas!) doesn't mean we can't still have our OWN children (they haven't outlawed gays from using turkey basters yet).
I didn't meet another child of divorce until I was in FIFTH GRADE. Nowadays, divorce is rampant. It's increasingly difficult to find couples who have stayed together. Amongst my friends, I can barely think of a few who are not children of divorce or who are not divorced themselves (some multiple times). Obviously, this is a problem in our society. Perhaps, we make it TOO EASY to get divorced. Before keeping more couples (the gay ones) from getting married, wouldn't a better protection for marriage be finding ways to make it harder for couples to give up on each other (though with so many people out there cheating on their spouses, which pretty much goes against the point of their being married to begin with, I'm not going to be the one to be able to offer a solution to stopping divorce).
Of course, while on the subject of cheating, I have to bring up another thought I've had...
...I've known quite a few men who were married to women, closeted, had children, and yet were GAY GAY GAY. I'll admit to my own sexual past of visiting bathhouses and glory holes (at the local adult video store) while sowing my wild oats as a younger, single man. I've bumped into men that I knew as customers who I'd seen in their day to day lives coming into my store with their wives (I''d even had sex with a few).
If gays get married and younger gay men can learn that they don't have to be miserable and pretend to be something they are not (except when they are away on business trips or happen to be in the men's room at the Minneapolis-St. Paul International Airport) there won't be as many men having sex at the bathhouses/glory holes/public bathrooms/highway reststops/public parks/etc. If gays get married, where will Sen. Larry Craig get dick? Will he have to pay for it like Rev. Ted Haggard? Of course, he may always bump into a man seeking sex because he's afraid of black men! Though, of course, even if gays can get married, single men may still harass their underage co-workers via e-mail/chat.
If gays get married, it will no longer be a stigma to be gay and merely marrying a woman will not be as much of a help to your political campaign or your career as a leading man. This will get away with the need for the "beard" or the glass closet...
(I don't want the owners of bathhouses/glory holes to get up in arms and fight gay marriage to protect their bottom line...their customers will certainly still be there. There will still be plenty of men who have NO desire to settle down.)
One of the ways they stigmatize homosexuality (and force us into a sexual preference ghetto) is to use the stereotype (perpetuated in our pop culture by such characters as Jack McFarland from "Will and Grace", Brian Kinney from "Queer as Folk" and Shane from "the L-Word") of homosexuals as beings who can not make a lasting commitment to a single partner and who have long strings of partners (while heterosexual culture ignores that same stereotype as applying to them with the same broad strokes when portrayed as Arthur Fonzarelli from "Happy Days" or Blanche Devereaux from "Golden Girls" for a couple of examples).
Of course, "they" will say they love the sinner, hate the sin. They mean that it's okay to be gay as long as we never have sex. We are meant to suffer in silence and practice celibacy for our entire lives, rather than live fulfilled lives. They preach to their heterosexual children to "wait until marriage" because pre-marital sex is a "sin". However, without being allowed to marry, we are forced to remain in the perpetual limbo of "wait until marriage" OR become the sinners they see us as. Why? To please THEIR religious beliefs (which brings us back into that same loop of what about the REST of Leviticus)...?
If gay is the new black, what will be the next gay? By removing the stigma of homosexuality, this removes the free ride for bigotry that we allow homophobes. After gays are excepted more by the mainstream, we'll have to move on to new prejudices. I'm sure that "they" will just move down the list to the Muslims, since they've been lining them up as the boogeymen/other for a while now, though the Muslims will likely be joined, ironically, by Atheists. Also, in Western culture, we continue to attack the obese and the willingly child-free. So, bigots, don't worry: You'll still have MORE people to hate/fear when you've moved on from the gays.