What's dangerous are the feelings that are generated with certain thoughts. Entertaining "what if" scenarios is fine as long as you are detached emotionally and realize you are just "entertaining". When feelings start getting involved, then the wall of objectivity is no longer there and your thinking transforms into believing. Since beliefs are based on "gut instincts" and I have found that my own "gut" is not trustworthy, I tend not to put a lot of stock in beliefs, both mine and other people's.

I think some people think that thinking a lot = intelligence. As someone who has disorganized, nonsensical thoughts, I can attest that this simply is NOT true. There is such thing as inefficient, wasteful, crazy-making thinking. But I don't think constructive thinking is ever bad. If your thoughts lead you to useful discoveries, then that is constructive. If your thoughts make your emotions spiral out of control? Destructive!