As always when there is a minority dissent the threads tend to overflow and overwhelm in favor of the majority position. I'll just reply to your most common objections and points.
1. Why do I care what two loving consenting adults do?
Because I don't want to glorify the gay union and allowing same-sex marriage elevates it to the same level as that between a man and a woman. It basically says they are the same family which is biologically and naturally inaccurate. The definition of family is at stake here. The point of marriage is to define what is a family in a conceptual way. You can have other types of families, gangs are typically and internally referred to as a family. But that doesn't mean they are the same type of family that is capable of producing and caring for off springs.
2. If it doesn't cause any harm why not allow it? A tired argument that is the same as referring to the bible as condemnation and refutation. It leads nowhere and is vapid. The absence of harm can't be the sole justification of something so polarizing and important as marriage. Also, where do we draw the line? Using that reasoning, we should automatically include incestuous relations. The line has to be drawn. A free society doesn't include unfettered freedom. There are actually plenty of prohibitions and conditions in western society.
Also, be aware that there is no such thing as a right to marry. It's a privilege. The are rights attached to a marital contract as well as obligations but there is no such thing as the actual right to contract. Privileges are by nature exclusive, they exclude others who don't qualify. The point of marriage is to preserve the family which is by nature defined as the sexual union between a man and a woman. This has nothing to do with individual capacity to bear children and is conceptual in nature.
Also, there is no coercion to marry. An opposite-sex couple can choose to live in cohabitation. Marriage is thus optional to define a family as a husband and a wife and any offspring.
