(BTW, you're wrong to distinguish between doubt
and thought: Descartes formulated the cogito
precisely because he viewed doubt as just a
particular kind of thinking, and so generalised
from doubt to thought. He actually started from
"I doubt therefore I am".)
I'm sure we all agree that to eliminate doubt in a
valid way would be ideal. The problem is that
there is no valid way, nor can there be one. We
cannot ever know that we know all there is to be
known. And as long as we believe that there is
more to be learned, doubt is an absolutely
essential tool in trying to do so.
Robin