The Zohar’s critical comment regarding Noach is not for the purpose of disparaging him, but is said in order to teach a lesson for our lives. The Talmud explains, that the Torah does not say negative things, even regarding animals. Undoubtedly, the Torah does not speak unfavorably concerning the righteous.
Torah did not speak disparagingly of an unclean animal, [would] it speak disparagingly of the righteous?
Talmud, Bava Basra 123a
Being critical of Noach is not to negate or discredit the way that he served G-d, but to allow us to learn from him. We are to take a lesson, that although in his generation he reached the greatest level achievable, in our times, we must take example from the manner of service that Avraham, Moshe, and Dovid introduced to the world.
We must stand up to the world because we possess the truth and wish to follow it, not because we are fearful—we must bring actual change to the world and not merely prevent its destruction—and last but not least, we should transform the world until it reaches a point in which it becomes one with G-d.
We should serve G-d like Avraham, Moshe and Dovid. Noach was only able to serve G-d in a way that related to the world. We, however, are able to surpass that level and serve the Almighty in a way that transcends the world.
(Based on Likutei Sichos 35, p. 15ff. Reworked by Rabbi Dovid Markel.)
