And there are a lot of reasons for marriage other than procreation.
There could be any number of reasons why people may get together and formalize their arrangements, but procreation is certainly the main reason that the state regulates marriage.
One man and one woman marrying and producing children and forming a family unit is the pattern that the state has a compelling interest in preserving. The state does it by supporting the traditional institution of marriage. I ask again: what is the compelling reason to change this state of affairs?
If the state indeed has an interest in promoting family life, then it should support the extension of marriage to homosexuals in order to stabilize and legalize their relationships. And as I pointed out to you, many homosexuals do have children.(as do many unmarried heterosexuals.)
In my experience discussing this issue, anyone who rabidly opposes gay marriage virtually always does so for two reasons 1) unthinking prejudice (I hate homos ) and 2) traditional religious teaching( God hates homos)
Any purported public policy rationales are just a pretext for (1) or (2) or most often (1) and (2)