I don't want to study his view (nor his Hegel etc.) so I'll just reply to your summary.
To summarise, he focuses on Zen At War
Firstly:
Without throwing Japanese Buddhism under the bus, it is a bit out there (i.e. atypical), both geographically and in other ways. It's the only form where priests can marry. I think it was influenced/altered by the State. But it's relatively famous in the United States.
Wthout throwing lay Buddhism under the bus, "Buddhism" in general e.g. as taught by the Buddha was more especially addressed to monks, including the Vinaya and so on.
Warfare, conquest, civil war, brigandry, serfdom, social inequality, economic exploitation, have existed in virtually every historical human society. The fact that warriors interpreted, adopted, adapted a religion to their own life is IMO no more an indictment of Buddhism than it is of Christianity, Islam, nor Atheism.
It reminds me of God Angrily Clarifies 'Don't Kill' Rule which was written in the aftermath of "9/11":
Humans don’t need religion or God as an excuse to kill each other—you’ve been doing that without any help from Me since you were freaking apes!
Maybe I should say this, if you use the particular (he focuses on "Zen At War") to criticise the general (i.e. "Buddhism" writ large).
But it's a bit of a trivial argument -- it's an example of "No true Scotsman":
- cw: Buddhism doesn't teach violence
- sz: The Samurai were violent
- cw: No "true" Buddhist etc.
I don't know whether he knows other aspects of Buddhism, nor why he "focuses on Zen At War".
That is, inner peace at the expense of acting morally
Is he setting himself up as judge? Is he saying, "Your behaviour is immoral, therefore you should have no peace, therefore anything which brings you peace is wrong"?
Because that doesn't sound like well-wishing, "I'm glad you found at least some peace."
And maybe too all-or-nothing, "If it didn't prevent all State violence then it's worse than useless."
Instead, who knows, maybe it was a net benefit morally. Many of the "101 Zen Stories" for example seem to me to be moral, meant to be exemplary.
an unsettled mind is sometimes appropriate over non-stop inner peace come-what-may
That sounds plausible -- but as Confucius once wrote, "For this reason I distrust plausible men."
At least two of the Zen stories look into the causes and consequences of anger:
The Gates of Paradise
A soldier named Nobushige came to Hakuin, and asked: "Is there really
a paradise and a hell?"
"Who are you?" inquired Hakuin.
"I am a samurai," the warrior replied.
"You, a soldier!" exclaimed Hakuin. "What kind of ruler would have you
as his guard? Your face looks like that of a beggar."
Nobushige became so angry that he began to draw his sword, but Hakuin
continued: "So you have a sword! Your weapon is probably much too dull
to cut off my head."
As Nobushige drew his sword Hakuin remarked: "Here open the gates of
hell!"
At these words the samurai, perceiving the master's discipline,
sheathed his sword and bowed.
"Here open the gates of paradise," said Hakuin.
Another is this, which is also about "emptiness":
Nothing Exists
Yamaoka Tesshu, as a young student of Zen, visited one master after
another. He called upon Dokuon of Shokoku.
Desiring to show his attainment, he said: "The mind, Buddha, and
sentient beings, after all, do not exist. The true nature of phenomena
is emptiness. There is no realization, no delusion, no sage, no
mediocrity. There is no giving and nothing to be received."
Dokuon, who was smoking quietly, said nothing. Suddenly he whacked
Yamaoka with his bamboo pipe. This made the youth quite angry.
"If nothing exists," inquired Dokuon, "where did this anger come
from?"
I find it difficult to see such doctrine as worthless. I think it's inline with some of the classic Buddhist doctrine
- He who checks rising anger as a charioteer checks a rolling chariot, him I call a true charioteer. Others only hold the reins.
I feel like the answer relates to emptiness not being no selves at all, but rather intersubjectivity: to do violence to others is to do violence to our other self.
You're not wrong
- All tremble at violence; all fear death. Putting oneself in the place of another, one should not kill nor cause another to kill.
That's not what "emptiness" means to me, though.
I think that "emptiness" is an extension of the non-self doctrine, expanding that to not just "the self" but to "all things".
"Emptiness" means, I mean I use my little understanding of it to say to myself something like, "those stupid reasons you had for acting stupidly are 'empty' and not worth holding onto" -- i.e. that both "conceits" and "views" (e.g. as explained here) are more-or-less fabricated.
I don't think that's meant to be instead of morality, used as an excuse to say that no-one exists and that it's impossible to be harmful, because I think that's explicitly a "wrong view".
There is admittedly also the story called Great Waves -- a bit of an odd one, more about a lay-person than a monk -- which tells of a wrestler becoming more powerful or less "bashful", less inhibited. I don't see that as an example of violence or immorality however -- nor of morality especially -- just professionalism maybe.