Leftism is the cause of mental illness, not the effect.
It's been a working theory of mine that the human brain is remarkably perceptive of truth vs. bullshit, far more so than most of humanity give it credit for. The consequence of this is that when the owner of that brain attempts to convince s/h/itself that something the brain has positively identified as bullshit is really the truth (fetuses aren't human, stealing from the wealthy will improve the economy,
#SpongeBrainShitPants's regime was honest, intelligent and ethical, etc. etc.) the brain breaks itself in order to attempt to comply with the impossible and conflicting demand placed on it.
Hence, the rampant mental illness among leftists.