Many heterosexuals do not see children as a defining characteristic of marriage. Marriage is very couple focused today. Its primarily seen as a celebration and acknowledgment that the couple is in a committed monogamous relationship. As such, people often marry after they’ve lived together for many years. They don’t even really see cohabitation as a trial marriage. The marriage doesn’t change anything really for them. It is primarily a status. The wedding is like a graduation ceremony. The marriage certificate is your degree. The civil benefits are seen to help the couple out. In fact, I do know some heterosexual couples who don’t get married because they get more state aid from the government if they are listed as a single parent.
Homosexuals want the same recognition. They want the same priviledges that come from being recognized. They want to go to a hospital and have people acknowledge that they have a close intimate relationship no different than a spouse and that they should be treated as a spouse.