Hakuin in one of his writings mentions the existence of heaven and hell, and asserts their reality. His reasons are not quite logical, and with the writings, at least as translated, there's more than a bit of defensiveness.
What to do with that?
Accept him at his word?
I do tend to subscribe to the ideas, as expounded by other Buddhists, that heaven and hell are what you make your life here and now. To be fair to Hakuin, he could be read that way, but that could just as well be a clever way around some statements that are hard to defend. It could be historical revisionism.
Generally, I tend to take a nontheist view of things; it is not important to the work of transcending suffering, curing the 3 poisons and so forth to speculate deeply about metaphysics. This comports with Buddhist viewpoints going back millenia, going back to the Buddha himself, who when asked about such things is said to have responded with a noble silence.
Hakuin couldn't have been totally ignorant of this, he was very learned to say the least, but his writing though could as well be informed by the Lotus Sutra, in particular where doctrines of upaya are presented. Quan-Yin/Kannon/Avolkitesvara will assume any form needed to accomplish compassion, if compassion is sought. Hakuin understood that there was a "popular" Buddhism that lay people followed because they could not afford the learning and leisure to practice zazen of the clerical class.
Hakuin was not above criticizing some of the abuses and decadence he saw in Buddhism of his time and place however.
I guess the difference is that between "thought leaders" - people who decide where to take culture by their unique position and leadership, and the masses, who don't have the time and leisure to consider deeply the spiritual, religious, political, psychological and otherwise "technical" (medical, scientific, legal...) aspects of the life they must live now.
So I want to make myself a bit clearer: I have nothing against any individual who decides to practice a 12 Step program, for whatever reason, if they think they need it. I even have nothing against those who, for want of a better solution, recommend a solution to a problem known to be suboptimal. But for those who are peddling known suboptimal solutions, based on snake-oil as some kind of universal optimum I modestly dissent, to use the words of the Scottish Calvinists in response to the Jacobites. When adherents of a sect claim some kind of metaphysical reality being breached uniquely to that sect, I have to respond: what is my experience, chopped liver? And when someone claims that their sect and its supporting structures has science behind hit, when there is none, I am compelled morally, I am acting ex cathedra, so to speak, from my vows to bring up what science is, why there is no science in the organization. And if there's a dodgy history behind the sect I will have to mention it. There's dodgy history in my sect, and I bring it up, should hucksters get a pass because they claim they "help people?"
The answer to my questions above, by the way, is to respectfully disagree with Hakuin's positions on heaven and hell, at least insofar as a noble silence on such subjects is disagreement.