Republicans and conservative Democrats want to extend them, the rest of the Democrats should be a little courageous and understand that they take little risk in voting against what the majority of citizens are also against:
A majority of Americans favor letting the tax cuts enacted during the Bush administration expire for the wealthy. While 37% support keeping the tax cuts for all Americans, 44% want them extended only for those making less than $250,000 and 15% think they should expire for all taxpayers.
...The debate Congress will have this fall will be over whether to extend the tax cuts for wealthier Americans. Most Republicans and some Democrats in Congress are thought to favor extending them for wealthier Americans. President Obama said Wednesday that he is opposed to any plan that would extend the tax cuts for wealthier Americans.
...With about one in three Americans, including a minority of independents and Democrats, in favor of extending the Bush-era tax cuts for all taxpayers, Democrats may not be putting themselves at great political risk by allowing the tax cuts to expire for wealthy Americans. In fact, the middle ground of extending tax cuts for low- and middle-income Americans but allowing them to expire for wealthy Americans -- the Democrats' most likely proposal -- is the specific option the public prefers most.
Gallup has typically found Americans unsympathetic to the argument that upper-income Americans are overtaxed. They generally believe upper-income Americans pay too little in taxes and favor higher taxes on wealthy Americans as a means to fund government programs, such as Social Security.
Meanwhile, the Republicans contend that $50 billion for infrastructure, which they were for before President Obama proposed it, is too much, while an $800 billion tax cut for the rich is fine.