The question is whether those on the left are gonna "advocate" for their liberal positions or if they are instead going to attack Democrats for not standing up for the liberal positions of the left.

The OP sorta claims that "we advocate for liberal positions and then we are accused of attacking the Democratic Party". Except what happens is not "advocating" it is attacking. You make an argument for "why the attacks are justified" but I was not necessarily arguing that the attacks are not justified. I am only saying that "they are attacks".

If liberals did more advocating and less attacking, then centrists would probably not be mad at them. If centrists are mad at them, then liberals have no one to blame but themselves.

Okay, that may have been uncalled for, that last line. I don't think Obama is the only one to blame though. Liberals on DU often post threads with the expressed intent of "expressing anger at Obama and making other liberals angry as well". Part of the reason Obama has lost liberals' support is because liberals are reading about all of his flaws and betrayals. The glass will never be 100% full and we will not get exactly what we want any more than FReepers did with Bush. It becomes hard to stay positive when one is bombarded with negativity. Is negativity a reality or is it a perception? A perception that is reinforced by a group.

Look, I share a desire to move both Obama and the Democratic Party to the left. I really do, but I don't think a strategy of constantly castigating them for not being progressive enough is a way to accomplish that. I think that if people came to DU and got information, they might walk away thinking "wow, single payer really is better" or "wow, Reaganomics really does suck (if I may put forward my own not so humble attempts in this regard http://journals.democraticunderground.com/... ). Instead they walk away thinking things like "wow, Obama and Democrats really do suck (thus why bother electing them)" or "wow, liberals really are arrogant and hateful". It seems to me we are our own worst enemy in moving the country in the right direction.