A person who thinks all the time has nothing to think about except thoughts. So he loses touch with reality and lives in a world of illusions. By thoughts I mean specifically, chatter in the skull. This is a disaster. For as a result of confusing the real world of nature with mere signs, we are destroying nature.
Like everything else is useful in moderation.
A good servant but a bad master.
And all so called civilized peoples have increasingly become crazy and self-destructive, because through excessive thinking they have lost touch with reality.