There are many reasons for this, but I will cite the top three:
#1. In a homosexual marriage, if a child is raised with homosexual parents, it will have a unequivocal effect on that child's morals, said child will be raised thinking that anything is OK, and morality does not exist, it would be like a drug dealer raising a kid, and saying that it doesn't matter.
The root of the homosexual problem is in the media, and how children are raised, this is proposing that we aid the gay agenda toward utterly eliminating moral law. Children must be raised in an environment were the parents are upstanding, and abide by moral law, so that the child will be moral.
#2. It takes the balance out of it, if you only have parents of one gender, it would take the balance out of it. Children would not know how to behave, only how their pervert parents behave, children must be raised in an environment with a dad and a mom.
#3. Gay people don't care for their children. There is no Oxycontin with them. Only crazy sex drive causing them to want to have sex with any one, any thing, any- anything.
If children are raised like this, it will destroy their morality.
Parents aremuch more to children what shepherds are to flocks. There can't be a child without a father and mother. The bond between parents and children is the strongest ever. Only the bond between lovers comes near. Without parents children are bound to suffer untold hardship and may go astray. One of the greatest desire of children who didn't grow knowing their parents is that of seeing them one day.
First and Foremost Children need a Mom and Dad because that's the Family Unit God Established. But below that Secular Studies show that Children do best with a Mom and a Dad. This is why even in cases where one Spouse cheat's on the other Spouse especially who have Children and the Spouse who cheated and come's to the other Spouse and say's their sorry and want's to restore their Marriage the other Spouse should work with the other Spouse to restore their Marriage since they made a Lifelong Vow to each other. Don't fall for the saying Once a Cheater Always a Cheater because people can accept Christ into their life's. Divorce is too easy and affect's Children since they don't have both their Mom and Dad together.
First off, there isn't anything that separates the genders, therefore the belief that the child would be imbalanced is terrible. Genders are not defined by their stereotypes.
Second, please keep your religious opinions out of debates, they dominate all of your thinking. What other reason is there to be against gay marriage? You think it's gross? Is that it? I think it's gross that you believe your God thinks it's just to want to bash other people for being born the way the were. Then again, I'M NOT TRYING TO TAKE AWAY YOUR BIBLES.
By the way, I'm not usually this rude, but there's an exception for people who think this way. @harrytruman
As long as the parents provide a stable and supportive environment for their kid(s), the gender makes no difference if that's what you're asking. Same-sex couples are just as capable of being as good as parents as heterosexual couples. Between a dysfunctional heterosexual couple and a stable and loving gay couple, which one would you pick? And if you're referring to single-parent households, I agree with what onemanitoban said.
What children need more than anything is a stable, reliable parent figure that they can form an emotional bond with, in a place that makes them feel safe. What will have long-term effects on a child is being trapped in a hostile environment. Children raised in a happy household by a functional single parent will turn out better than a child raised in a dysfunctional married household rife with abuse and conflict.