He's advocated for a complete expiration of the Bush tax cuts, like Howard Dean. While thats a minority position in the progressive community, its not a tiny minority. The thing is Jeffrey Sachs is completely baffling on his stands on fiscal policy, and has had run-ins with Krugman and Delong. On budgetary matters he's very liberal, he's advocated for a budget that has higher tax rates and slashes defense, while putting more government involvement into the healthcare system like a Public Option along w/ the ACA.
But you would think someone with that view towards budgetary matters would favor Keynesian counter-cyclical fiscal policy, but he hates that. He's also a big time deficit hawk and is anti-keynesian. He was against the Recovery Act and American Jobs Act, and for the same reasons: they are short-term spending that will excarcerbate our deficit outlook and not fix the structural problems with our economy. He calls ANY stimulative measure simply re-inflating the bubble while harming the deficit.
So it makes sense for him to want all tax cuts to expire because he's less concerned about the economic impact rather than the structural change the revenue would bring to our budget outlays. In fact, for someone like that, the fiscal cliff is probably an ideal budget package.
As a matter of math, I agree with Sachs that longterm, even the 1.6 T in revenue that Obama was initially asking for is not enough to protect the Social Safety net from harm in the future. You would need at least 2 T along with big cuts in defense. Since big cuts in defense will be tough, its safe to say 2.3-2.4 T would be the number to reach.