I believe that censorship is mostly being pushed by Senator Conroy himself, who comes from the Catholic, Social Conservative right faction of the party (For non-Australians: the left-wing Labor party is in power in Australia, with the support of a number of independents. Conroy is a member of the Labor party, but isn't from the trade-unions and is regarded as right-wing. He's also very socially conservative for Australia. For example, he opposed the RU486 "morning after pill" on a conscience vote
http://www.australiavotes.org/conscience/index.php#vote)
There's no doubt that Fielding likes the plan too, but don't expect to disappear while it is in Conroy's portfolio.
I've never heard of the internet filtering being a carbon-tax bargaining chip before. Given that it was planned before Labor supported the carbon tax I'd be surprised if it planned that way.
(Also, note that this is technically voluntary filtering by these ISPs, so it probably wont' go away even if Conroy left)