- mental illness isn't real, all problems are societal and don't stem from the brain
- people who treat mental illness are shills for "Big Pharma" which is only out to make money and poison people with drugs that don't do anything but harm people
- psychiatry is a form of societal control out to quash anyone who deviates from what they deem as normal, while psychiatric diagnoses (in the DSM) are made up on a whim and are just stigmatizing labels
Many antipsychiatry activists are consumer-survivors who've experienced abuse in the mental health system or believe they might be harmed if they were treated. They are frequently paranoid and are very, very rigid about their beliefs, and obnoxious about sharing them. Scientologists are another type, and antipsychs also exist among academics and even psychiatrists.
Antipsychiatry activists are commonly found online commenting in forums and on the blogs of people who write about mental health, admonishing people to throw out their pills and renounce treatment. Although their primary peeve is with psychiatrists and psych medications (and they're especially opposed to ECT), some protest against talk therapy and psychological research too.
At the core, the argument is really about mind-body dualism.
"Oh, they're antipsychiatry activists. Joe runs into them all the time in his online depression support group. They keep telling him that his antidepressants don't work and he should throw them away."