Everyone but Tenzin backed Tarrlok's discriminatory laws against non-benders. In "The Voice in the Night," when Tarrlok proposed his anti-Equalist task force to the Council, he referred to "all us benders" while addressing them. In the following scene, Amon referred to the Council as "the bending oppressors." And apparently the "Republic Tour" feature on the interactive TLOK website confirms that all the councillors are benders, according to the Avatar Wiki. And that's the crux of the problem. Remember the backstory established in the first episode: Aang and his friends founded Republic City to be the bastion of unity and balance in the world, but in the 17 years since Aang's death, the city has lost its way and fallen out of balance, leading to widespread poverty, gang violence, the domination of benders at the expense of non-benders, etc. The fact that the current Council consists entirely of benders is a sign of how far things have fallen out of balance.