“Because marriage is an equal partnership.”
So the issue with man-dog is that it doesn’t meet the traditional definition of marriage?
Why are you so limiting the definition? I would define marriage as a person committing to a loving relationship with a being he loves.
Frankly, from what I have seen when bestiality, incest and polygamy are brought up, the pro-gay-marriage position has been to get huffy and offended that you would compare them to these obviously perverse and problematic relationships.