I've tried googling why it is bad but it says nothing about it being bad. job wise, the employer can't legally ask about mental health unless sits going to be dangerous at work. and that if employers do ask about it, it can be classed as discrimination?

It is not bad unless you say it makes you suicidal or want to harm others.

90% of people in this stressful world experience mental health problems. Mild to severe symptoms it’s certainly not bad to have on your medical record. However some people in my own opinion have limited knowledge of mental health and think it’s something really bad it’s all just stigma. Take care

I think it mostly has to do with the stigma surrounding it. A lot of people, even medical professionals, don’t understand and think they are made up or think people with mental illness are crazy, etc. Also, down the road if you commit a crime or want to own firearms, there might be a possibility they could expose that/blame things on mental illness or prohibit you from purchasing firearms (I’m not saying that’s a good or a bad thing). In some cases you might be deemed mentally unfit for certain positions, probably especially political positions as that has happened in the past. Of course medical records are confidential and landlords and employers can’t ask you about your mental illness. This is just speculation, though. I think the benefits of diagnosis, particularly correct diagnosis, outweigh the disadvantages.