Gay marriage activists would like us to think that allowing gays to marry would have no effect on the rights of others, and that children raised in such marriages suffer no ill effects. They use flawed studies that are guided to try to prove their point. In fact, the opposite is true. Allowing gay marriage tramples on the religious rights of those who feel that homosexual activity is against the laws of God. And studies show that children raised by homosexuals do indeed suffer ill effects from that upbringing. (This article will deal with the latter; click on the above link to go to the article regarding religious rights.)
Significant research on families shows that children do best in low-conflict marriages with their biological parents. Aspects of homosexual marriages or unions are highly unfavorable to the healthy raising of children. 
Homosexual relationships tend to be unstable. Studies show that about 75% of homosexual couples either plan for or tolerate sexual liaisons with other people. Infidelity always brings about negative effects for the family, especially for children. Homosexual relationships also tend to be short-lived.
The homosexual lifestyle is highly oriented towards having numerous sexual partners. (A. P. Bell and M. S. Weinberg, in their classic study of male and female homosexuality, found that 43 percent of white male homosexuals had sex with five hundred or more partners, with 28 percent having 1,000 or more sex partners.) The brief encounter is part of this lifestyle for male homosexuals, and for females, group sexual play is common. Engaging in sex with numerous partners increases the risk of sexually transmitted diseases, and also damages the psyche of participants. (See the article on promiscuity.)
The sexual acts of homosexuals tend to be unhealthy and can often lead to illness. This risky behavior shortens the lifespan of homosexuals and sets their children up to be orphans. (In a major Canadian centre, life expectancy at age twenty for gay and bisexual men is eight to twenty years less than for all men.)
Homosexuals model a poor view of marriage to their children, who themselves have to grow up and form relationships. Children can be confused, and have a tendency to enter into homosexual relationships themselves, even when the biological tendency is absent. Homosexual relationships put sexual intimacy into the role of pleasure rather than procreation, so the entire plan of God and nature is thwarted.
Acts of violence are more common in homosexual relationships than in heterosexual. Psychological abuse is also more common.
Perhaps partially due to the stigma of homosexuality and gender confusion during their youth, homosexuals tend not to be as mentally balanced as their heterosexual counterparts as they mature.
Statistics show that homosexuals have a greater tendency to abuse alcohol and drugs.
Studies are showing that incest is also more common in households with homosexual parents.
Fathers and mothers deal differently with children and studies show both influences are needed. The most successful parents are heterosexual.
“In a democratic society, those who choose to cohabit in “alternative” familial arrangements such as same-sex unions have the freedom to do so. But toleration is one thing; promotion and “celebration” are another. To entrust children to such arrangements is wholly beyond the pale. As history shows, a society that champions such unions at the expense of traditional families does so at its own peril. But with the formidable forces of nature, culture, and history arrayed against them, such efforts to remake the most fundamental institution of society are not likely, in the end, to prevail.” 
[For sources, click on the end notes and go to the bottom of the page.]