I don't think George Lucas ever intended Yoda to be seen as a hero. However, every kid, if not every adult, who's ever seen a Star Wars movie has dreamt of being a Jedi, and Yoda is the embodiment of that seemingly romantic era when the power of the Jedi was absolute. Thing is, the prequels gradually presented us with quite a different image of the Jedi than that which the kind face of Luke Skywalker originally symbolized.
The Old Order
Think of what the Jedi really were under the old order when Yoda headed the council. Without all the pomp and circumstance, they were ultimately a religious order that brainwashed a small portion the galaxy’s children for centuries. They did this under the pretense of raising these children to be the next generation of Jedi knights — a life they were not guaranteed despite having been indoctrinated with Jedi ideals since infancy, endangering any chance of a normal life for them outside the Jedi order should they be cast out.
The Jedi removed Force-sensitive babies from their families with no regard for their mental well-being, forced them to train with lethal weapons as toddlers, and shunned them should they experience or exhibit human emotions that are a part of every child’s growth into a healthy adult.
Imagine being 4 years old, cast out of the only family you've ever known because you threw too many tantrums. Or 14, completely alone in the world because you weren't chosen to be a Padawan learner. #Yoda watched this take place, personally tutoring generations of younglings for near a century, and for one deemed so "wise" he somehow never, in 900 years, considered that treating children this way was wrong?
Every other Jedi, even the eldest members of the council, would have been trained from infancy by Yoda.
Similarly, the use of the Kamino clones only furthers Yoda's disregard for humans. He allowed these men to fight for the Republic despite the questionable morality of allowing people that have been brainwashed since birth — and have never had any autonomy of their own — to fight and die for you.
'As Wise As Master Yoda...'
Yoda: “Fear is the path to the dark side. Fear leads to anger. Anger leads to hate. Hate leads to suffering.”
Anakin Skywalker dubbed Yoda as the wisest of the Jedi, but when exactly did Yoda offer anything truly insightful? Yoda is not only unhelpful in his supposed "wisdom" much of the time, but very often hypocritical. He talks of how fear is the path to the dark side, and yet he fears the dark side so much that his students, for 900 years, have been shielded from all knowledge of it.
Anakin, a slave boy raised in complete and utter poverty and removed from his mother at age 9, was told he was not allowed to be fearful or angry. Those suppressed emotions are what festered and formed the part of Anakin that became Darth Vader. There's a kind of poetry in that Yoda was, in fact, right — except it was not only Anakin's fear that paved his path to the dark side, but Yoda's as well.
Yoda: "Do or do not. There is no try."
Yoda continuously spreads negativity and passivity paraded as wisdom. He presents his Jedi with a binary world, a world where there is only the good and the bad, with nothing in between — a totally unhealthy view. The Force is not a coin with two sides — one light, one dark — but more like a lake that gets deeper and darker the father you walk in. Go too far and the darkness will swallow you. Anakin was meant to find the center, but Yoda, in his fear and distrust, would barely let his Jedi do more than paddle in the shallows.
Yoda asks the impossible. You cannot have compassion without attachment. He raises his students to care for everyone, then berates them for forming attachments. In a way, he raises these children to remove their own humanity.
The image above from Return Of The Sith shows Yoda telling Anakin, if unknowingly, that he should "rejoice" at the impending death of his wife. This very conversation is what put Anakin in the perfect position to be corrupted by Darth Sidious. This is illustrated through the choice of lighting in this scene, in which Anakin's face is shrouded heavily in darkness, with light only hitting a small portion of his face.
The Jedi spoke of the chosen one bringing balance to the Force, but they never tried to find that balance themselves. Yoda never let Anakin explore any kind of balance within himself, so fearful of Anakin's potential for darkness. Perhaps with a less oppressive upbringing, and mentors who'd let him work through his anger, Anakin would have been strong enough to turn away from the darkness and become the hero both Qui-Gon and Obi-Wan believed he could be.
The prequels, despite their faults, do contain a very vital lesson: Ignorance and passivity are the pillars of evil, just as much as fear and anger (perhaps even more so). After all, anger and fear often win good causes where ignorance and a passive nature never can. Yoda is not the personification of what a Jedi should be, he is an example of what terrible thing a Jedi can become when he places some false sense of moral supremacy over what is actually important.
Do you agree that Yoda is less than exemplary of the Jedi way?