Anakin proved the idiocy in the Jedi way of thinking. For all their wisdom, not one of the Council members stopped to say, 'hey, has anyone noticed the balance is WAY in our favor? There are thousands of us, we basically do what we want, and there might be like one Sith guy somewhere, maybe. Why would we want to make it even??'
but no. And the rest is history.
The Jedi weren't out of balance. Read Lucas' quote.