Studies on Leftists:

Leftists are mentally ill
"Extreme liberals had a 150% increased rate of mental illness compared to moderates."

Leftists are miserable
"We found that right-wing (vs. left-wing) orientation is indeed associated with greater subjective well-being."

Leftists are emotionally unstable
"The higher neuroticism (or lower emotional stability) evinced by more liberal individuals in both studies is related to many negative outcomes and characteristics, including the predisposition to experience negative affect, higher sensitivity to negative mood inductions, lower relationship quality, and lower performance motivation."

Leftists have low disgust sensitivity
"We demonstrate that individuals with marked involuntary physiological responses to disgusting images are more likely to self-identify as conservative. This relationship holds even when controlling for the degree to which respondents believe themselves to be disgust sensitive."

Leftists have incomplete moral foundations, are individually rather than group-focused
"Liberals consistently showed greater endorsement and use of the [individualizing] Harm/care and Fairness/reciprocity foundations compared to the [group-oriented] foundations [Ingroup/loyalty, Authority/respect, and Purity/sanctity], whereas conservatives endorsed and used the 5 foundations more equally."

Envy, selfishness, egalitarianism, and willingness to harm the innocent predict support for wealth redistribution
"Controlling for age and gender, support for coercive economic redistribution is predicted by envy, self-interest, communal fairness, and willingness to inflict instrumental harm. Compassion, while strongly motivating support for redistribution, neither motivated nor protected against coercion."

Narcissism and psychopathy predict anti-hierarchical aggression
"[Anti-hierarchical aggression] was associated with antagonistic narcissism and psychopathy. However, neither dispositional altruism nor social justice commitment was related to left-wing anti-hierarchical aggression. We assume that some leftist political activists do not actually strive for social justice and equality but rather use political activism to endorse or exercise violence against others to satisfy their own ego-focused needs."

Machiavellianism, narcissism, and psychopathy predict victimhood signaling
"The virtuous victim signal can facilitate nonreciprocal resource transfer from others to the signaler. Individuals with Dark Triad traits more frequently signal virtuous victimhood. A form of narcissism that reflects a person's belief in their superior prosociality predict more frequent virtuous victim signaling. The frequency of emitting virtuous victim signal predicts a person's willingness to engage in and endorse ethically questionable behaviors."

Virtue signalers are hypocrites
"Self-reported moral character predicts moral double standards among reputation-seeking individuals. Claiming oneself as a moral person does not always translate into doing good deeds, but can manifest as showcasing one's morality to others."

To save others, Leftists are willing to kill innocent Whites but not innocent Blacks
"Political liberals were more likely to endorse consequentialism when the victim had a stereotypically White American name than when the victim had a stereotypically Black American name. When given both the [White] and [Black] scenarios, participants were strikingly consistent in their use of consequentialist or deontological principles, such that their responses on the second scenario almost always mirrored those in the first."

Being exposed to anti-White ideology makes Leftists more anti-White
"While social liberals were overall more sympathetic to poor people than social conservatives, reading about White privilege decreased their sympathy for a poor White (vs. Black) person. Moreover, these shifts in sympathy were associated with greater punishment/blame and fewer external attributions for a poor White person's plight."