They accept what they are told because it makes sense at a superficial level.
Deep thinking is hard work. And sometimes it is depressing.
Better to just avoid deep thinking and accept what you are told if it sounds good.
It's like what Hannah Arendt said about Adolf Eichmann and the banality of evil (i.e., he wasn't necessarily evil as much as shallow and clueless--a joiner).
Satan’s useful idiots.
I think you are on the right track, and it fits with what the “study” underlying the article actually proposes.
Doubtless there are a narcissistic and mentally ill radical elements out there, on the Left and Right. But the vast majority of lefties are shallow morons pursuing what they believe is their self-interest, under the influence of political manipulators and social pressure. People with low intelligence, low self esteem, and low emotional self-control are likely to be simultaneously unsuccessful, eager for someone to blame, open to promises of something for nothing, dependent on others to run their lives, and easy to con.
The Democrat Party has always favored coercion to freedom (slavery, Jim Crow, New Deal), and has evolved its program, messaging, tactics, and even the voting system, to use morons to stay in power.