I don't think they are gullible as they are intellectually lazy. They are willing to let other think for them. The MSM helps by only presenting one side of the argument. They sit around and are too lazy to investigate the other side remaining perfectly willing to believe what they see and hear.
I am of the belief that liberals are divided into two groups.
One group is dissatisfied with their financial lives. (class envy)
Whether rich or poor, they are jealous that someone has more than them, and instead of looking inward, they demand that the government punish the successful because they are convinced everyone is cheating... or whatever nonsense.
The second segment has a deep-seated dislike/hatred toward the Judeo=Christian morals which have guided our great country the past 225 years.
They feel soooo guilty at their own 'rule-breaking' & depravity, that they try and eliminate all politicians who promote upstanding, clean living (for lack of a better description).
That is why so many young people vote Democrat, because lets' face it, we tend to act out sexually & socially when we are young... and then return to our parents' morality as we grow older. (that's what I did, sort of)
Some certainly are, while many decidedly are not. I think a more common trait is their need to feel that they are "good" people. Even more important is for others to view them as good people. As many others have observed, it is largely unimportant to them to actually do good so long as they can feel that they have good intentions.
The more assertive liberals take the next step and seek to affirm their sense of superiority by coercing everyone else within reach to conform to their transient definitions of what it is to be good. In other words, they are being obnoxious power mad jerks.