If you can be talked out of your principles by Joe Leiberman, or any other person looking to defeat public healthcare... THEN YOUR PRINCIPLES MEAN NOTHING.
I'll say that again - if you are willing to lay down your principles because of something Joe Leiberman tells you that "you gotta do", then YOUR PRINCIPLES MEAN NOTHING.
There's a lot of very good, very moral Democratic politicians. I'm sure they have some very respectable intentions.
Intentions don't matter if you will completely set them aside at the request of someone looking to counter those intentions.
It's like a voter who intends to vote in a way that will push for public healthcare - if they are willing to put that aside to vote for someone who won't push for that, but will use soothing words anyway... then the voters intentions don't matter - they're acting in a way that kills public healthcare.
If the party doesn't end up acting, good intentions won't count - people who actually care about public healthcare, like me, will reasonably conclude that voting for these politicians is a vote against healthcare. It is a vote that says that your principles don't matter, and that you will settle for getting less than nothing.