Ah, but "gay marriage" permits them to push for acceptance of their perversion in the church. The "right" to have same sex ceremonies at churches, to be listed in the church directory as a "family". All counter to biblical teachings.
While all sinners are welcome in the church, they should not expect to change the church and encourage such sin. Go forth and sin no more.
Civil Unions also allow a "standing" to claim joint tax filing as a right, social security survivor benefits as a right, and immigration spousal visas as a right of the petitioner.
Democrats DO support all of the above and Kerry wrote on his website that he supported all of the above. Very different from GWBush.