Neither the positive or the negative definition you provide for quixotic stands on its own, it's the combination of the two that gives the word it's unique meaning. Something quixotic is simultaneously ambitiously idealistic and hopelessly unrealistic. It's not quixotic if it isn't both.

Neither the positive nor the negative definition you provide for quixotic stands on its own: it’s the combination of the two that gives the word its unique meaning. Something quixotic is simultaneously ambitiously idealistic and hopelessly unrealistic. It’s not quixotic if it isn’t both.