[Casiopea]

Originally Posted by Andrew

...'read' is therefore, somehow, agentless so

The book reads easily = the book is easy to read

then by the same argument,

The food likes easily = the food is easy to like
the film enjoys easily = the film is easy to like
the job hates easily = the job is easy to hate
the dog catches easily = the dog is easy to catch

are all grammatically correct.

The first three are suspect: the data is contrived. Food, film, and job are inanimate; they cannot like, enjoy, or hate and, moreover, the verbs like and enjoy are linking verbs, whereas hate is not (See note below), so the first three sentences are not examples of mediopassive voice. They are not 'grammatical', to use your word.

In mediopassive voice it's the object that's promoted, not the subject. In other words, promote the object ball and the result is a mediopassive-voice reading. (Note, the symbol ? means semantically awkward):

Active: The dog catches the ball easily.
Passive: The ball is caught easily.
MedioP: The ball catches easily. (Dogs, in general, can catch the ball easily.)
Compare MedioP with:
Active: ?The ball (itself) catches (things) easily.
Middle: ?The ball catches, itself, easily.

Active: Max catches the dog easily.
Passive: The dog is caught easily.
MedioP: The dog catches easily. (People, in general, can catch the dog easily)
Compare MedioP with:
Active: The dog (itself) catches (things) easily. <The dog is the agent>
Middle: ?The dog catches (itself) easily.

Notice that, in active The dog (itself) catches (things) easily, the agent is the dog; the dog does the catching, whereas in mediopassive The dog catches easily, the dog doesn't do the catching; it is the thing being caught.The agent is left unstated. Active and mediopassive, and even
middle, might look the same on the surface, but they're structurally different. That's why your last example, mediopassive The dog catches easily works.

Active: People read the book well. <Note, you could use easily (enough)>
Passive: The book is read well by People.
MedioP: The book reads well. (People, in general, can read the book well.)
Compare MedioP with:
Active: ?The book (itself) reads well. <The book is the agent>
Middle: ?The book reads (itself) well.

Notice that, mediopassive The book reads well, the book is not the agent; the book doesn't do the reading; the book is experienced by an agent left unstated. In active ?The book (itself) reads well, the book is the agent; it does the reading, which is why it's semantically awkward: books don't read themselves.

In short, those examples (active, mediopassive, and middle) are identical on the surface level (i.e., what we see and/or hear) but they are structurally different at the underlying level. Now, could that non-linear factor be the reason you seem to be getting an active or middle voice reading from mediopassive The books reads well? The reason I ask: up to this point no one has been able to support the argument that mediopassive read is not contrived.

All the best.

Note, Sam hates easily is active voice (Sam hates people/things easily), and not mediopassive voice. If it were, it would be paraphrased as People, in general, can hate Sam easily, which is a different meaning.

In fact you can't get a mediopassiev reading at all. The verb hate subcategorizes for a doer as subject; i.e., the one doing the hating. So, as long as the verb is active in appearance, which is the case with mediopassives and middles in English, the subject will always be interpreted as the one doing the hating, even if the object is promoted:

Active: People hate vegetables easily.
Mediopassive: ?The vegetables hate easily. <Awkward because the vegetables are the ones doing the hating.>

Active: Sam hates Max easily.
Mediopassive: ?Max hates easily. <It has an active reading only: Max is the one doing the hating.>