While I basically agree with you, I am also strongly of the opinion that the Democrats are doing what they know to be a lie to dominate the Congress and win the Presidency.
I remember a reporter around the time of the Bush Sr Presidency. He asked a number of questions of Congressmen (all anonymous) whether, after four years of the Reagan Presidency, they were now firm believers that tax cuts help the economy and increase employment; that reducing business taxes to zero would stimulate business and increase tax receipts; that eliminating the death tax would be fair; that eliminating capital gains taxes would stimulate business further; and that allowing businesses to expense capital investments in the year the investment was made, and not spreading it out over 3, 10, 20 years, would be a huge boon to business.
A huge majority of the Democrats interviewed said privately, not for attribution, that they agreed. But they all avowed that to say so publicly would be political suicide, and refused to ever acknowledge such publicly.
I think we remain in this same position today. Dems want political power so badly that they will say things detrimental to the American economy, and American security, so as to win office. Not only for tax policy, but for negotiating with terrorists (rather than killing them); handouts to voters (healthcare, college, bonuses for babies); reducing defense budgets (thereby reducing our security); giving amnesty to illegals.
I wish it was true that all Dems were just stupid morons, like the most prominent examples in their party -- Patty Murray and Dick Durban being most notable. But I honestly believe that they are deliberately duplicitous.