Yvor Winters's book In Defense of Reason (1947, combining critical essays from three earlier books) contains very strong criticism of Ralph Waldo Emerson.
Early in the book, he criticises Romanticism in general:
The Romantics, however, although they offer a relatively realistic view of the power of literature, offer a fallacious and dangerous view of the nature both of literature and of man. The Romantic theory assumes that literature is mainly or even purely an emotional experience, that man is naturally good, that man's impulses are trustworthy, that the rational faculty is unreliable to the point of being dangerous or possibly evil. The Romantic theory of human nature teaches that if man will rely upon his impulses, he will achieve the good life. When this notion is combined, as it frequently is, with a pantheistic philosophy or religion, it commonly teaches that through surrender to impulse man will not only achieve the good life but will achieve also a kind of mystical union with the Divinity: this, for example, is the doctrine of Emerson.
Winters also describes the Romantics and Emerson as relativists:
The Emersonian formula is the perfect one: that is right for me which is after my constitution; that is right for you which is after yours; the common divinity will guide each of us in the way which is best for him.
This conflicts with Winters's own view of literature, which he calls "absolutist". Winters
believe[s] that the work of literature, in so far as it is valuable, approximates a real apprehension and communication of a particular kind of objective truth.
After quoting a few lines of verse by Emerson, Winters comments harshly,
Just how much Emerson meant by this passage it would be hard to say; it is always hard to say just how much Emerson meant, and perhaps would have been hardest for Emerson.
This criticism is soon followed by the following summary of Emerson's doctrine (see also the romantic reliance on impulses mentioned earlier):
If there is no possibility of error, the revision of judgment is meaningless; immediate inspiration is correct; but immediate inspiration amounts to the same thing as unrevised reactions to stimuli; unrevised reactions are mechanical; man in a state of perfection is an automaton; an automatic man is insane. Hence, Emerson's perfect man is a madman.
On the same page, Winters adds:
The Emersonian and allied doctrines differ in their moral implications very little from any form of Quietism or even from the more respectable and Catholic forms of mysticism.
In another essay included in the book, "Maule's Curse, or Hawthorne and the Problem of Allegory", Winters also criticises Emerson before turning the Hawthorne' work:
Emerson eliminated the need of moral conviction and of moral understanding alike, by promulgating the allied doctrines of equivalence and of inevitable virtue. In an Emersonian universe there is equally no need and no possibility of judgment; it is a universe of amiable but of perfectly unconscious imbeciles; (...).
In the essay "Jones Very and R. W. Emerson. Aspects of New England Mysticism", Winters makes the following comment on Emerson's influence:
Emerson was the most influential preacher to appear in America after Edwards, for the lecture platform was merely the ultimate step in the secularization of the pulpit, a step that was inevitable after Unitarianism had displaced Calvinism, and Emerson, moreover, succeeded in focussing upon his romantic amoralism a national religious energy which had been generated by a doctrine and by circumstances now equally remote.
The essay contains many other criticisms of Emerson, for example,
Emerson at the core is a fraud and a sentimentalist, and his fraudulence impinges at least lightly upon everything he wrote: (...).
In "Maule's Well, or Henry James and the Relation of Morals to Manners", Winters states that the "anti-moral philosophy" of Emerson and other romantics had a "corrupting influence" [in New England].
In the book's "Post Scripta", he adds,
Now I respectfully submit that only a minute portion of what has been written on Poe or Emerson or any other subject has any considerable value, and that a good deal of what has been written and very respectably published is unmitigated twaddle; (...).
This is because, as Winters explained in the preceding paragraphs, many Emerson specialists are unfamiliar with the works of his contemporaries and many American Poe specialists are unfamiliar with the French symbolists.
Winters does not use the phrase "sacred cow" in In Defense of Reason, but he claims that Emerson did not really understand what he wrote (or if he did, he refused to live by the principles he preached), that the Emersonian universe was "a universe of (...) imbeciles", that the man was a fraud, etcetera. These are very outspoken attacks on Emerson's doctrines and reputation.