My mental illness has the trait of black and white thinking. I can also be direct. In my personal experience, one does not have much to do with the other. I struggled with black and white thinking even in my younger days, when I had more issues expressing my opinion. I struggled perhaps even more when I wasn't honest and direct with people.

I think someone already mentioned tact, and I will agree. Being direct needs to be tempered with tact or it can be a problem. I'm not always great at this. It's when I don't read the situation and still speak up that I tend to find myself not very popular.