And the idea that the whole discussion can take place from a kind of 'Buddha's-eye-view', above the whole fray of human weaknesses and faults, and untainted by moral corruption, can easily be used to justify immoral behaviours - as it is in this thread.
It also ignores all the canonical literature, which Zen claims as its own, which goes on at length discussing transgressions, precepts, wholesome karma, unwholesome karma, etc...
People can dismiss all of it though by deferring to a purported higher wisdom which they either explicitly or implicitly claim to possess. If your Master, who you claim is enlightened, possesses such wisdom then in the Zen context they are in a privileged position to employ "miraculous function" 妙用 with which to prompt awakening in others (this can include otherwise irrational and immoral actions).
Your own liberation is in their hands and as an article of faith you depend on them as a prerequisite for liberation, hence the excuses for reprehensible behaviour. You have faith that the individual in question is just educating people in unorthodox albeit worthwhile ways, and predictably make charitable excuses for them and/or attack anyone criticizing them for failing to understand what is really
Basically, people who make excuses for such immoral behaviour can claim to be unattached to phenomena all they like, but they are actually quite clearly emotionally invested in their teachers and organizations. The psychology of past investment is key to understanding their behaviour -- they've put in a lot of emotion, energy and perhaps material and monetary resources into their religious pursuit, master and spiritual family, so pulling away becomes all that harder when you have to admit failure and loss.