I wrote an essay addressing many of these issues awhile back, and ask you to have a look if you have time.
One would be perhaps foolish to argue that a few bad apples spoil the whole bunch. One would be perhaps foolish to assert that someone who, perhaps, had an affair while married is to be lumped into the same category as rapist or a child molester. One would be perhaps foolish to assert that a teacher with a family propensity to alcoholism is thus to be completely written off as a teacher (and would be perhaps foolish to discount the possibility the the weakness will strengthen his or her ability to speak to fellow human beings dealing with addiction issues).
In fact, the vast number of Zen and other Buddhist teachers I know are kind, gentle, non-violent, honest folks who are genuinely decent people who live what they preach (same for the vast majority of Catholic and Christian clergy, despite the bad ones).
One would be wrong both to throw out "all the babies with the bath water", and one would be foolish to demand saints of 100% of the clergy 100% of the time. (The only reason, I believe, that old religious books ... Buddhist, Christian and any other ... contain images of "Perfect Saints" is that they have been scrubbed of any hint of human failing after the "religious hero" died in a process of hagiography. That is not to say that there were not truly saintly, truly moral people in all religions throughout history ... but that few people are not without some imperfections.). I would rather study Buddhism's teachings on managing human imperfections with someone who has managed his or her imperfections well, then with someone who had never any at all or denies them artificially.
I reject the premise that this is an issue limited to any one branch or branches of this or any religion. A 5 minute search through Google will reveal similar abuses and "fallings down" by members of the Theravada Sangha, human beings too ...
All human beings, from 'Great Bodhisattvas' right on down to the rest of us, are human beings ... and that means rough edges, cracks and ugly spots, flesh, fallings down and flaws. (At least, of course, until we eventually become Perfect Golden Buddhas ... assuming that even those ideals reside anywhere beyond our flawed human imaginations) Human beings are human. That includes Zen and other Buddhist teachers, no less.
What matters most is what we do with those flaws in life, how we live as human beings ... with a bit of grace, ease, non-attachment, wholeness, peace, at-oneness and sincerity, great Compassion and Loving Kindness toward our fellow flawed beings. Practice does not remove all our human rough spots, but it allows a wild and imperfect stone to be imperfect (perfectly imperfect) yet simultaneously material to be polished into a jewel ... so many rough edges made soft and round. The Precepts are a guide for constant moment-to-moment practice in "not falling down". One cannot polish a tile into a Buddha ... but the constant polishing is Buddha.
Yet, despite the roundness and polishing, some rough edges may remain. All human beings have the tendency to fall down from time to time, some more than others.
It is a fallacy to think that Zen or other Buddhist priests are ever completely free, during this life, from being human. In any large group of people ... whether Zen priests, other Buddhist, Christian or Jewish priests and clergy of all kinds ... there will always be examples of greed, anger and ignorance. Furthermore, in the lifetime of any one individual ... even among the best of us ... there are sure to be moments of greed, anger and ignorance.
But our Practice does, more often than not, free us from the worst. It makes us better people. (In fact, most clergy I have met ... not just Buddhist clergy, but of all religions ... are good, caring, ethical people, the bad apples aside). Most of the Zen teachers I have met ... especially those with a few years and some maturity under their belt ... tend to be lovely, gentle, well rounded, self-actuated, moderate, compassionate, healthy people - balanced, living life with fullness and well.
What is more, a teacher can be 95% good, wise and decent, a caring and profound minister ... yet have a proclivity in the remaining 5% that is an inner devil. The fact is that being a Buddhist teacher has not allowed many to avoid getting led around by the "little Buddha" in their pants sometimes, getting involved in sex scandals. There have been several modern Buddhist masters with addiction issues. I do not know of any case of child abuse involving a modern Zen or other Buddhist teacher ... but I would not be shocked if there ever was such a scandal. I know of Zen teachers who have punched other Zen teachers, or momentarily "lost it" and taken to an instant of violence.
The question is whether the 95% that embodies Wisdom and Compassion is completely canceled and nullified by the 5% which is an ass and a human fool. Certainly, if the 5% is serious enough (child abuse as seen among some rabbis and priests is certainly an example, as are other acts of violence or truly malicious conduct), I say it does, certainly. (In fact, while recognizing that even the victimizer is too a victim of beginingless greed, anger, ignorance ... toss the worst of them in a cell, and throw away the key!). On the other hand, if what is seen is a relatively minor human weakness or failing ... I say it does not. What is more, it may make the teacher an even greater teacher because of his/her humanity.
In other words, I would rather learn about some things from a fellow weak and fragile human being wrestling, right now, with Mara than from a stone Buddha statue, a Dharma machine, a Flawless Saint (although how many of those long dead saints and ancestors in religious hagiographic story books, their lives cleaned up and dipped in gold and set on a pedestal after their deaths, were truly so flawless during their flesh and blood lives?).