Why did George Washington worry that Shays's Rebellion would "render ourselves ridiculous" in the eyes of all of Europe?

George Washington was worried about this because he knew
that most people in Europe did not think that the United States would really be able to
function as a country.

In those days, most thinkers were of
the opinion that a country with a system of democratic government could never last.  It
was believed that such a system would fall apart because it lacked a real leader. 
Washington worried that Shays's Rebellion would show that the US's experiment in
democracy was falling apart just as the Europeans thought it
would.

Because of this, Washington worried that the
rebellion would confirm the predictions of the Europeans, and prove that a democracy
could not last.