The fact is that an ETS is electoral poison in the medium to long term and Labor knows it. That is why they will only negotiate with the coallition on this - they need the coallition to back it otherwise they will lose power over it.
Nobody in the general public realises how economically disastrous this will be, forcing investors away due to sovereign risk concerns and energy price concerns, not to mention the gigantic losses due to government monetary churn. And all for what? A mere 5% of 2% of world emissions.
If an ETS or carbon price ever goes through it has to be with bipartisan support. Rudd knows it, Labor knows it and the Liberals know it.