You can argue that Venus and Mars are both planets but you can’t argue they are the same. Our description of Venus is much different from our description of Mars. And so it is with marriage and same sex unions.
No one can argue against creation and say that a man's parts and another man's parts were designed to fit together. No one can argue with creation and say that a woman's parts and a another woman's parts were designed to fit together. And no one can deny that a man's part and a woman's part were indeed designed to fit together.