Same sex marriage will obviously lead to people marrying animals.
It will also lead to group marriages where three or more individuals will want to marry each other.
Soon people will demand the right to marry things such as rocks or trees or caves.
Then people will fall in love with mountains, forests and rivers, and want to marry them.
This will lead to persons wanting to marry landscapes and entire ecosystems including vast herds or buffalo or wildebeest..
.. which will lead to the ultimate disaster: humans falling in love with the earth and wanting to live in peace with it ’til death they do part.