I have always been bothered by anti-stigma campaigns. When I see them, I often start having dehumanizing thoughts about people labeled as "mentally ill". The thing is, anti-stigma campaigns push the belief that "mental illnesses" are chemical imbalances that can only be fixed with medication. Also, the campaigns tell people to separate "mentally ill" people from their "mental illness", but I find a difficult time doing that. The thing is, humans define other humans by their mental traits. As a result, saying that "mentally ill" people are sick and can't get better without directly altering their brains makes us scared of "mentally ill" people. We have an instinctive reaction to avoid disease. Since calling their brains sick makes think the person is a disease on a subconscious level (even though consciously we know that is absurd) as we define people by their mental traits, we start fearing and othering "mentally ill" people.
We could do better by realizing that some "mental illnesses", like anxiety and unipolar depression, can be completely resolved without trying to alter our brains directly, like having someone work with us to change our thought patterns or making lifestyle changes. The brain is a plastic organ, so our mental function is not biologically predetermined. Other "mental illnesses" that cannot be resolved, such as ADHD, are likely to just be differences that only give people trouble because they live in a world that is not adapted to their needs (by the way, this viewpoint is also called the social model of disability). People aren't really diseased; they just aren't living their lives in a way that is helpful to them, and either they need to change the way they live or society has to be changed so that they can live in a way that works for them. Society is mad, not them, and many so-called mental health issues is an understandable response to our kind of society.