The stigma is there (and will remain there until we prevent mental illness) for several reasons:

#1: Negative, agitated and/or out-of-control people are a pain in the a$$ to deal with.

#2: No one has been able to find the line between "mental illness" and being a selfish brat, or being weak or just having a terrible personality. And the diagnoses for things is very subjective and people have gotten dozens of different diagnoses from different care providers. Who do we trust?

#3: If all mental illness was really "biological" than therapy shouldn't help. And the pharmaceutical companies have been caught in so many lies for profit that they've lost people's trust. Look at that Oxford study last month saying that antidepressants don't work for kids/young adults and cause lots of harm and the previous studies were funded by Big Pharma and were lies.

#4: The trank 'um and toss 'um on the street approach is not what anyone would call cutting edge treatment. Insurance companies increasingly don't want to pay for therapy and finding a therapist with actual wisdom is like finding a needle in a haystack. And most psychiatrists don't even know how to help people safely withdraw from medications, which makes them a menace to society.