Well let's start off with the fact that marriage has already gone through a fundamental transformation over the ages. It started off as a business deal exchanging a piece of property, the woman, from her father to her husband in exchange for money, livestock service. It is now a civil contract between two consenting adults. If someone wants to have their marriage blessed and performed by a priest, minister, rabbi or imam then they are free to do so.
As the effect on children the American Academy of Pediatrics has weighed in on the subject stating;
“The academy’s new policy statement says same-sex marriage helps guarantee rights, benefits and long-term security for children, while acknowledging that it does not now ensure access to federal benefits. When marriage is not an option, the academy said, children should not be deprived of foster care or adoption by single parents or couples, whatever their sexual orientation….”
“The academy cited research finding that a child’s well-being is much more affected by the strength of relationships among family members and a family’s social and economic resources than by the sexual orientation of the parents.“There is an emerging consensus, based on extensive review of the scientific literature, that children growing up in households headed by gay men or lesbians are not disadvantaged in any significant respect relative to children of heterosexual parents.”
Opponents of marriage equality are simply trying enforce their own beliefs on others.
Sounds like you are trying to enforce your views on others.