Constitutionally indefensible Obamacare is an enormous document, made to be deliberately confusing. This was undoubtedly so that activists could interpret it any way that they wanted to.
And as big and ambiguous as it already is, Constitution-ignoring lawmakers are effectively making it even bigger with this additional legislation.
No one's yet invented the magic wand that you can wave to repeal Obamacare. Therefore we need to win elections to repeal it. To do that, you get Dems on record voting against something as voter-friendly as this legislation and then run ads telling how they voted a year from now. If it passes, then we take credit for introducing it.