Mental health is the most complicated science field since it reaches to the core of how we've shaped ourselves and our surroundings for our entire existence.
So ignorance is to be expected in an overview manner.

But when it comes to the humane manner, the ignorance is harmful.
Instinctively, people feel comfortable when they know someone has a problem confessed, because of competition to feel and be seen as strong. Labeling someone with a mental illness or a personality disorder increases comfort in the masses knowing that they are not in fault in the struggle, yet creates a major downfall for those who have been labeled.
I will re-explain a part of what I said - If someone is labeled with a mental illness or personality disorder, people blindly relate most negative things feeling from them as having to do with their label/s. It gives non-diagnosed or unfamiliar people the increasing comfort knowing that they have absolutely no problem in the struggles (I have experience with an arrogant big brother and an emotionally down-putting father to back me up).
The truth is - people cause each other "mental illnesses". It's not just genetics. People instinctively bully those different "genetics", and Psychology apathetically gives "Because that's how it is" explanations, such as "Humans show hostility towards strange people so the tribal order can continue". I hate those explanations because they ignore the fact that most of us are far away from tribal constructs. And even if we are, are we really just going to accept this apathetic explanation and say "Oh ok, it's normal that some people fall into suffering, because that's our nature"? Because if that's the case, we won't make the planet a better place as High-Tech company so desirably love to spiritually broadcast.