One reason is that being a Wobbly I believe our old motto ‘A injury to one is a injury to all’. Solidarity is important even if it hasn’t really worked out so far.
Another reason is I think the conservatives are right; marriage equality will subvert traditional marriage. Of course I think subverting traditional marriage is a good thing. After a promising start subverting traditional marriage in the 1950’s and a very intensive period from the late 1960’s to the late 19700’s we haven’t made much progress in subverting traditional marriage lately. Marriage equality seems like a useful way to rev up the process again. I want to totally de-privilege marriage and see society value all forms of family.
Lastly I have the luck to be living in California. We already have fully inclusive state ENDA, hate crime and anti-bullying laws. In states without these protections I would say that a fully inclusive ENDA should be first priority. Our survival is far more important than marriage equality can ever be